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1. lt 18 gt lt 16 gt lt 19 gt lt 26 gt lt 255 gt lt 12 gt lt 9 gt lt 3 gt lt 33 gt lt 8 gt 2 lt 43 gt lt 30 gt lt 14 gt lt 13 gt lt 21 gt I T lt 31 gt lt 32 gt lt 34 gt lt 22 gt lt 23 gt lt 35 gt lt 29 gt lt 52 gt Description Returns grating and slits to original factory calibration Adjusts the entrance and exit slits to the CSR value and sets the mono to the CSR mode Remote handshake byte lt 27 gt yes This command prompts the user to Enter the Calibration value in the current units Changes made using this command will erase the values preset at the factory This command allows the user to enter a new wavelength Press the Enter key to complete this command Returns the current grating ruling identifier Changes grating if additional gratings are installed This command returns the grating to the home position This command allows the user to enter the wavelength Scans faster than slewing the grating towards the longer wavelength until the DK receives a 24 or reaches the limit of the grating operation Scans faster than slewing the grating towards the shorter wavelength until the DK receives a 24 or reaches the limit of the grating operation Returns the serial number of the monochromator Slews the grating towards the longer wavelength until the DK receives a 24 or reaches the limit of the grating operation
2. Slews the grating towards the shorter wavelength until the DK receives a 24 or reaches the limit of the grating operation This command resets one or all slits Returns the current slit width Adjusts slits to a given width Sets the scan rate at which the grating rotates during Scan operation Returns the current scan speed Steps the grating motor one step towards UV Steps the grating one step toward IR Adjusts entrance slit only Adjusts the exit slit only Adjusts the middle slit on DK242 only Allows for entrance slit calibration Allows for exit slit calibration Allows for middle slit calibration on DK242 only Returns the current wavelength setting Sets the current wavelength to 0 00nm The Cancel byte lt 24 gt sometimes preceded by a status byte terminates operation of the Digikr m This does not apply to the Echo and Reset commands A status byte is used to indicate errors or status information SH Spectral Products ii 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lym Spectral Products Operation 3 4 GPIB IEEE 488 Interface Option The IEEE 488 Bus General Purpose Interface Bus provides an electrical and mechanical system for interconnecting electronic measurement devices With the GPIB Interface Option installed the monochromator can be controlled by any GPIB controller All GPIB commands are echoed back to the controller The echoed commands have an apostrophe
3. appended at the beginning and end of the echo word Setting the Digikrom GPIB address The GPIB address of the monochromator can be set to any address between 1 and 31 To set or reset the GPIB address press the OPTIONS key while the READY screen is displayed on the Digikrom Control Module The control module will display the following OPTIONS 1 CALIBRATE 2 REMOTE 3 GRATING Press the 2 key to display the REMOTE screen The display will then show the following 1 REMOTE MODE 2 SET GPIB ADDRESS Press the 2 key again to set or view the GPIB address The display will show GPIB ADDRESS x ENTER 1 31 X is the current GPIB address Input the desired GPIB address between 1 and 31 and press the enter key To exit without changing the GPIB address press the back arrow key lt or the ENTER key if no address has been input Press any key except RESET to return the monochromator to manual control operation Timeouts After initializing the GPIB interface card set the timeout to longer than 180 seconds If only one grating is installed in the monochromator the timeout can be set to 90 seconds or longer The longer timeout allows the monochromator to perform a Grating select routine before a timeout error can occur For more information on sending and receiving GPIB commands see GPIB demonstration program provided with your monochromator GPIB status bytes are returned in ASCII form as defined below The status by
4. Mid Byte gt lt Low Byte gt DK240 480 Action If 65536 lt High Byte gt 256 lt Mid Byte gt lt Low Byte gt in hundredths of nm is a valid position then the scale factor used in determining position will be recalibrated to make the current position agree with the input position The grating will return to home after completion From DK240 480 Status Byte gt From DK240 480 lt 24 gt p SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 oS Spectral Products Operation GOTO This command moves the monochromator to a selected position Valid values of position are grating dependent and are described in Appendix C To DK240 480 lt 16 gt p From DK240 480 lt 16 gt p To DK240 480 High Byte gt Mid Byte gt lt Low Byte gt DK240 480 Action If valid grating will move to 65536 lt High Byte gt 256 Mid Byte gt lt Low Byte gt in hundredths of nm From DK240 480 Status Byte gt From DK240 480 lt 24 gt p For example the command to instruct the monochromator to GOTO the wavelength 250 nm could be sent as the 4 bytes lt 16 gt p 05 p lt 97 gt p 1685 p units are in hundredths of nm Here lt 16 gt p specifies the GOTO command While 05 p lt 97 gt p 1685 p specifies the destination of 25000 in hundredths of nm GRTID Returns the 6 byte current grating ruling identifier To DK240 480 195p From DK240 480 lt 19 gt p From
5. 2 Disp SLOT WIDTH Entering 1 will display MONOCHROMATOR IS lt gt RESETTING lt gt OPTIONS This command offers 3 menu commands to change the active grating enable Remote mode or calibrate Recalibration In the event that you feel the instrument needs recalibration this can be initiated from the control module or external computer via the RS 232 cable At this point the monochromator must be set to a known wavelength that you have determined by means external to the DK240 480 laser atomic line etc NOTE Grating calibration should only be performed after grating zero is checked and if necessary re zeroed using the OPTIONS command The OPTIONS command offers three functions Remote Calibrate or Grating Once selected each option has submenus that will prompt the user for information Pressing the will exit the OPTIONS mode and return to the READY screen OPTIONS 1 CALIBRATE 2 REMOTE 3 GRATING When the 1 key is pressed the display changes to 1 CAL GRATING 2 ZERO 3 CAL SLITS 4 CLEAR The Zero command will make the current grating position 0 0nm Press 2 the unit will zero and the display will return to the READY screen SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Operation Go to a known wavelength and press OPTIONS press 1 press 1 again The display will read IS MACHINE ALI
6. By selecting the TEST function By removing power from the instrument SO LUMO SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Sp Spectral Products Appendix F Reference Drawings F Reference Drawings Optical Diagram of DK240 480 As indicated above light from a source is focused on the entrance slit and directed by the turning mirror M1 to the collimating mirror C The focused beam is collimated and directed to the grating G which diffracts and reflects the radiation A particular wavelength of the light determined by rotation of the grating is directed to the focusing mirror F which focuses it onto the exit slit via the second turning mirror M2 Optical Diagram of DK242 5A Spectral Products j 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 KS Spectral Products Appendix F Reference Drawings EXIT ENTRANCE SOURCE As indicated above light from a source is focused on the entrance slit and directed by the turning mirror M1 to the collimating mirror C The focused beam is collimated and directed to the grating G which diffracts and reflects the radiation A particular wavelength of the light determined by rotation of the grating is directed to the focusing mirror F which focuses it onto the exit slit via the second turning mirror M2 Optical baffles are utilized to minimize stray light due
7. 208 0245 Fax 505 298 9908 Lym Spectral Products Operation 2 3 Product Specifications 2 3 1 DK240 480 Wavelength Drive Worm and wheel with microprocessor control Bi directional Design Czerny Turner triple grating turret Focal Length 240 480 mm F 3 9 7 8 Gratings 68 x 68 mm ruled are standard Holographics available Wavelength Precision 0 01 nm with 1200 g mm grating Wavelength Accuracy 0 3 nm with 1200 g mm grating Scan Speed 1 to 1200 nm minute with 1200 g mm grating Maximum Resolution 0 06 nm with 1200 g mm grating Slits Computer controlled Width 10 to 3000um Height 2 to 20 mm Software Demo control program with source is included A LabVIEW Driver is available upon request Power UL listed 110 220 V power pack meets or exceeds UL1950 CSA 1402C and IEC 950 Interface RS 232 standard Warranty One year from delivery date CE marked 2 3 2 DK242 Wavelength Drive Worm and wheel with microprocessor control Bi directional Design Czerny Turner triple grating turret Focal Length 240 mm F 3 9 Gratings 68 x 68 mm Ruled are standard Holographics available Wavelength Precision 0 01 nm with 1200 g mm grating Wavelength Accuracy 0 3 nm with 1200 g mm grating Scan Speed 1 to 1200 nm minute with 1200 g mm grating Maximum Resolution 0 06 nm with 1200 g mm grating Slits Computer controlled Width 10 to 3000um Height 2 to 20 mm Software Demo contro
8. a scan This is useful for example where measurement of a constant interval of frequency is desired spectral power distribution measurements With the exception of slit setting operation in the CSR mode leaves the other functions unchanged When the monochromator is positioned using GOTO or scanned using SCAN the slit widths will be continuously and automatically adjusted to provide constant bandwidth The spectral dispersion of a monochromator is frequently quoted in units of nanometers per millimeter of exit width However the spectral dispersion is a function of wavelength The spectral dispersion will change by about a factor of two as a single grating is scanned over its full range When a monochromator with fixed slits is scanned over a wide wavelength range the change in spectral dispersion will change the bandwidth of light that is passed by the fixed slits In the Constant Spectral Resolution mode CSR a changing slit width compensates for the changing dispersion to maintain fixed spectral resolution Instead of selecting fixed slit widths the user selects a fixed bandpass At each wavelength the Digikr m then sets the slit width to allow the preselected bandwidth to be maintained Some important limitations apply to this method 1 First the effective entrance and exit slit widths may be limited by the source and detector If the source is imaged on the entrance slit and if that image width is less than the slit width then cha
9. at half maximum FWHM measured for a single monochromatic line Ideally the resolution is limited by the number of illuminated grooves on a grating N providing the grating is uniformly illuminated A AA lt N In practice however the resolution is typically limited by slit widths dispersion and optical aberrations in the system SH su Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lm A Spectral Products Appendix I Theory Other physical factors that may be external to the system can also impact resolution Since three data points are needed to define a peak a monochromator made to take large scanning steps will show a triangular peak if it doesn t miss the peak altogether The FWHM of this triangle will be wider than could be seen by taking finer steps A similar effect limits the resolution of array coupled spectrographs where the minimum image size per data point is equivalent to a single pixel At least three pixels are needed to define the monochromatic peak so the FWHM becomes limited to value of 2 3 pixels widths multiplied by the RLD Since there is no benefit to send multiple entrance slit images to the same pixel the entrance slit should be set to a width no narrower than one pixel width Bandpass Monochromator The FWHM is also called the bandpass as it defines what band of wavelengths is passing through the spectrometer Most often the term bandpass is reserved
10. diffracts the light into component wavelengths A slight rotation of the grating causes a change in wavelength transmission For a fully illuminated grating the resolution of a grating or ability to distinguish between two wavelengths is given by the following equation AA 2 or AA L Example with 1200 gr mm 30mm wide 600nm N dW A 600 1200 30 017nm if grating is full m order N total number of grooves illuminated A wavelength at slit W grating width mm d is groove density in gr mm Grating Equation l 2 cos g sin 8 nd Where d is groove density in gr mm p is the Ebert angle This is a fixed angle determined by the position of the grating the collimating mirror the focusing mirror It is approximately 189 99 for the DK240 480 0 is the angle that the grating rotates measured from the point at which white light is specularly reflected through the instrument 70 is the maximum grating angle for the DK240 480 The DK240 480 grating drive provides a minimum AO of 0075 n is the order of diffraction For light incident normal to the grating some of the light will be reflected diffracted to the right 1 order and diffracted to the left 1 order Diffraction at greater angles also occurs but it is not significant orders 2 3 SH Spectral Products ii 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Sp Spectral Products Appendix B Encoding Decod
11. given brightness watts cm steridian the maximum power watts that can be coupled into an instrument is the product of the brightness and the etendue This is true because the brightness of a source cannot be changed changing the apparent emission angle changes the apparent size in inverse proportion The brightness a LaGrange Invariant is unchanged For a monochromator the etendue is E Sw Sh Wg f where Sw slit width Sh slit height Wg grating width F instrumental focal length In a chain of optics or optical instruments the component with the smallest etendue will determine the etendue of the system For spectrometers it is useful to find the spectral energy density watts nanometer that can be coupled This can be found by dividing the etendue by the spectral bandwidth D E Sw A D Sh f Wg A where A is the angular dispersion of the grating The ratio of usable slit height to focal length is approximately constant across all monochromators it is limited by aberrations Therefore the spectral energy density depends primarily on the grating width and secondarily on the dispersion To get the maximum throughput use the widest highest dispersion grating available Etendue defines the coupling between a light source and a spectrometer Transmission efficiency describes the light loss within the spectrometer The transmission efficiency becomes T Rm Rg where Rm is the reflectance of a sing
12. opposite to the first grating then the angular dispersion of that second grating will subtract from that of the first grating The net dispersion is zero Now the entrance and center slits determine the bandpass Because the dispersion at the exit slit is zero its width has no effect on the bandpass Subtractive dispersion is useful in imaging applications and in pulse studies In trying to relay an image through a single monochromator the image is distorted by the angular dispersion that exists at the exit slit This angular dispersion is cancelled in the subtractive double In pulse analysis a single monochromator will cause temporal broadening because of the unequal path lengths for light at the grating In a subtractive double these unequal path lengths are cancelled For users who wish further information we recommend the review article by Murty or Hutley s book on diffraction gratings Specific questions about the DK series can be answered by the staff at SP SH Spectral Products 9 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lym A Spectral Products Operation Entrance i I Image f Intensity Wavelength Fig 2 1 Formation of a spectral line As the image of the entrance slit approaches the exit slit there is no light exiting the monochromator As the entrance image starts to overlap the exit slit opening the output intensity increases until the maximum output is attained
13. optical spectrometers use diffraction gratings as the wavelength dispersing element The diffraction grating has a series of parallel grooves spaced at about the wavelength of light Each groove diffracts the incident light and interference between the diffracted light from each groove allows only one wavelength at each angle Amazingly gratings with as few as five grooves show the properties of diffraction gratings With the grooves of the grating perpendicular to the plane of incidence light incident at angle i is diffracted at an angle r for wavelength lambda n lambda d sin i sin r where d is the grating groove spacing and n is the order of the diffraction see Figure I 3 SH Spectral Products ki 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Appendix I Theory Grating normal Incident light Bisector Diffracted light Figure I 3 Diffraction by a grating Light is incident at angle i Light is diffracted at angle r The sum of l and r is a constant 2 phi in a monochromator Theta r I is the angle of rotation from specular reflection The preceding discussion is a simplification neglecting the optical aberration resulting from a less than perfect image of the entrance slit Nevertheless the model provides a good foundation for understanding the properties of monochromators and spectrographs as discussed below For a more detailed treatment see M V R
14. read READY 00100 0nm SW 0050p SS 0100nm m The keyboard consists of 21 keys 11 control keys and 10 number keys including a decimal point The numeric keys are used to enter parameter values in response to prompts from the LCD display The LCD display will prompt the user to enter a value The user responds by pressing the appropriate numerical keys and the decimal point key for wavelength operations correcting erroneous entries with the backspace key Once the displayed value is correct the user then presses the ENTER key and the entry is accepted by the controller Please note that the numerical entries must agree with the units indicated by the LCD prompts The command keys are used to initiate or halt the many functions of the Digikr m 240 480 The keyboard layout is shown above Described below are the various command key functions of the Digikrom monochromator 5A Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Operation MANUAL This command allows the user to change the rotation of the grating by one motor step It also allows the user to set a new zero position for either A equal to zero or a nonzero value The MANUAL key shifts control of the grating table back and forth between manual and automatic When the user shifts from AUTO to MANUAL mode by pressing the MANUAL key the display responds by replacing the word READY with MICMAN M
15. right 1 order and some will be diffracted to the left 1 order Diffraction at greater angles also occurs but is not significant orders 2 2 3 The DK240 grating drive provides a Dq of 7 5 x 10 3 degrees Because entrance slit images are formed at different angles for different monochromatic wavelengths different wavelengths will be exiting the monochromator at different angles The grating causes an angular dispersion as a function of wavelength and this angular dispersion is preserved at the exit slit SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Operation In a single monochromator the angles at which light strikes the grating is independent of wavelength In the second half of a double monochromator the angle at which the light strikes the grating depends on the wavelength The first grating has introduced angular dispersion as a function of wavelength If the second grating rotates in the same direction as the first grating then the angular dispersion of that second grating will add to that of the first grating The dispersion is doubled If the entrance center and exit slits are approximately the same width then it is the entrance and exit slits that limit the bandpass Because the dispersion at the center slit is half of that at the exit slit the bandpass of the center slit is twice that of the exit slit If the second grating rotates
16. slits must be set to a known width by a method external to the monochromator before recalibration The most practical method is diffraction pattern measurement whereby laser light is passed through relatively narrow slits and the main beam of the diffraction pattern is measured Place a white card in front of the spherical mirror nearest the slit being calibrated and observe the laser diffraction Properly calibrated slits will have a main beam of 12 7mm for a DK240 or DK242 and 25 4mm for a DK480 when the slits are set to 25 3 3 Remote Operation The Digikrom 240 480 can be controlled by any remote computer that has an RS 232 serial communications port The controller can be left in series with this port connection 1f desired by pressing the OPTIONS key on the controller and selecting 12 REMOTE Total control over the grating table and continuously variable slits can be achieved through a simple protocol The RS232 connection requires a cable with a DB25 M subminiature connector to connect to the monochromator and a computer communications port connector at the other end as appropriate for the user Spectral Products offers a DK24AT DK24PS DK24MA and DK24IC cable for connecting to AT PS2 MAC style computers and GPIB respectively Pin Assignments for the Female DB 25 Connector at Ends of DK240 480 Pin NAME FUNCTION 1 GND Chassis Ground 2 TxD Data in from computer to DK 3 TxD Data out f
17. when the entrance slit image perfectly overlaps the exit opening As the entrance image continues past the exit slit intensity decreases until there is no light exiting when the entrance image has gone completely past the exit slit SH Spectral Products di 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Operation 2 7 Calibration and Errors in Monochromators Spectral Products monochromators use a two point calibration method that is the zero order point and one wavelength The zero order point can be determined using virtually any light source broadband or monochromatic diffuse or coherent since the grating is acting essentially as a mirror at this point The slits are taken down to their minimum aperture typically 10 um and then the grating position is adjusted to produce maximum throughput The zero command then stores this location into non volatile RAM the number stored is the number of motor steps from the device s physical home position determined by location sensors on the grating turret and motor shaft to the optimized optical zero order point The second point can be calibrated at almost any arbitrary wavelength usually chosen to be somewhere in the middle of the particular grating s spectral response The monochromator compares its actual physical location with the ideal location for that wavelength in terms of motor steps from zero to produce the cali
18. www cvilaser com DK Recovery Disk Used to restore SP factory offset values to your monochromator or spectrograph ee 2 2 Hardware Connections Power is supplied to the DK240 480 by the power supply a Attach the power cord to the three prong outlet on the back of the power pack Attach the connector from the power supply to either end of the monochromator c Plug the power cord into your wall or power strip outlet The monochromator will reset in approx 3 minutes and find home position The monochromator can be controlled by an optional handheld controller or with a computer To control the monochromator from a computer only connect the standard serial interface RS 232 cable not a null modem cable from the computer directly to the monochromator 25 pin connector located at one end of the monochromator To control the monochromator from a computer or from the controller connect the control module to the monochromator body and then connect the personal computer to the female DB 25 connector on the controller The OPTIONS key on the controller will allow the user to switch to the REMOTE mode the personal computer When controller is in the REMOTE mode the protocol of Chapter 3 page 12 should be used To return control back to the controller press OPTIONS again The monochromator will reset and the controller display will return to the Ready screen SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877
19. 480 lt 29 gt p From DK240 480 lt High Byte Mid Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action The current wavelength is 65536 High Byte 256 Mid Byte gt Low Byte in hundredths of nm From DK240 480 lt 24 gt p ZERO This command sets the current wavelength to 0 00nm CAUTION Use of this command will erase factory settings To DK240 480 lt 52 gt p From DK240 480 52 p To DK240 480 lt One byte p DK240 480 Action The current zero offset values of the gratings are saved as the zero order position and sets the current position to 0 00 nm From DK240 480 Status Byte gt From DK240 480 lt 24 gt p lt One Byte gt For the DK240 480 the one byte is always 1 for the DK242 the one byte can be 1 or 2 SH Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Operation 3 2 Hand Held Controller DK2400 The DK2400 Handheld Controller sends command instructions to the DK240 480 Single Low High Step Speed Speed SOURCE ZABON SUT MANGAL f ADJ 3 2 1 Operation The DK2400 receives power from the monochromator Connect the controller RS232 cable to the RS232 connector at one end ofthe DK240 480 Once the controller receives power the control display will read MONOCHROMATOR IS RESETTING The DK240 480 will find home position and the control unit display will
20. DK240 480 Byte 1 gt lt Byte 2 gt lt Byte 3 gt lt Byte 4 gt lt Byte 5 gt lt Byte 6 gt 1 number of gratings installed in the monochromator 1 3 2 number of grating currently in use 1 3 3 high byte of current grating ruling g mm 4 low byte of current grating ruling g mm 5 high byte of current grating blaze wavelength nm 6 low byte of current grating blaze wavelength nm From DK240 480 Status Byte gt DK240 480 Action No action From DK240 480 24 p GRTSEL This command changes gratings if additional gratings installed To DK240 480 lt 26 gt p From DK240 480 lt 26 gt p To DK240 480 lt One Byte gt 1 2 or 3 depending on gratings installed From DK240 480 Status Byte gt DK240 480 Action If valid slews to new grating and automatically resets From DK240 480 lt 24 gt p RESE This command returns the grating to home position To DK240 480 lt 255 gt p lt 255 gt p lt 255 gt p DK240 480 Action Grating will return to home position SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 oS Spectral Products Operation SLIT RESET This command resets one or all gratings to home position To DK240 480 lt 43 gt p From DK240 480 lt 43 gt p To DK240 480 lt Slit Byte gt 0 All slits 1 Entrance slit 2 Exit slit 3 Middle slit DK242 only From DK240 480 Status Byte gt DK240 480 Action One or all slits will return t
21. Digikrom DK 240 Meter DK 242 Double 4 Meter DK 480 4 Meter Monochromator Spectrograph User Manual Document 1049461 e January 2003 Hl Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Ep Spectral Products Table of Contents SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Introduction 3 1 1 Mission Statement 3 1 2 Warranty 3 1 3 Copyrights 4 1 4 Product Overview 4 Getting Started 5 2 1 Verify Shipping Contents 5 2 2 Hardware Connections 5 2 3 Product Specifications 6 2 3 1 DK240 480 6 2 3 2 DK242 6 2 4 DK Series Specifications 7 2 4 1 Wavelength Accuracy 7 2 4 2 Resolution 7 2 4 3 Wavelength Precision 7 2 4 4 Slits 7 2 5 Software 7 2 6 Theory Of Operation 9 2 7 Calibration and Errors in Monochromators 12 Operation 13 3 1 Command Summary 13 3 2 Hand Held Controller DK2400 21 3 2 1 Operation 21 3 2 2 Error Screens 27 3 2 3 CALIBRATING ZERO WITH A HANDHELD CONTROLLER 28 3 2 4 CALIBRATING AT A WAVELENGTH WITH A HANDHELD CONTROLLER 28 3 2 5 Slit Calibration 29 3 3 Remote Operation 29 3 4 GPIB IEEE 488 Interface Option 31 A Wavelength Ranges 33 B Encoding Decoding Data Bytes 34 C Status Bytes 36 D Novram Program Calibration Procedures 37 E Constant Spectral Resolution CSR 39 F Reference Drawings 41 O
22. GNED YES ENTER NO Press ENTER If you want to exit this step press and you will return to the Ready screen Pressing ENTER will display ENTER DESIRED A ENTER A nm You then enter the externally established wavelength and the DK240 480 adjusts its calibration point then performs a hardware reset At the end of the reset cycle the new calibration will be in effect If problems are encountered during this procedure consult SP for assistance Limits have been set on the extent to which you can alter the factory calibration of the DK240 480 If the display indicates the desired calibration parameter is too large or too small then the method for determining the calibration point should be reviewed Grating limits are shown below Groove mm Limit um Groove mm Limit um Groove mm Limit um 3600 500 600 3000 75 24000 2400 750 300 6000 50 36000 1200 1500 150 12000 20 80000 Grating Select Blaze Pressing the OPTIONS key on machines with 2 or 3 gratings will produce the following screen OPTIONS 1 CALIBRATE 2 REMOTE 3 GRATING Pressing the 3 key will display GRATING 1 SELECT 2 GRATING ID BLAZE Pressing the 1 key will produce the following screen if the machine has 3 gratings and is currently using grating 1 CURRENT GRATING 1 NEW GRATING 1 3 Pressing the appropriate key 2 or 3 will rotate the appropriate grating into position and initiate a reset sequence When the READY screen reapp
23. ICMAN A 00100 00nm 1 SW 0050u SS 0100nm m In MANUAL mode the wavelength of the monochromator is controlled by pressing selected keys on the numerical pad The numbers on the top row 7 8 and 9 control the scan speed in the increasing wavelength direction and the numbers on the bottom row control the decreasing wavelength scan speed The numbers on the middle row have no effect on the scan The 7 or 1 number key in each row produces a single step each time it is pressed The 8 or 2 number key in each row produces a continuous scan at one half the scan speed as long as the key is pressed The 9 or 3 number key in each row will scan at the speed shown in the display The user can return control to the AUTO mode by pressing the MANUAL key again and the display will replace MICMAN with READY All other keys with the exception of the 1 2 3 7 8 9 and MANUAL keys will have no effect on the status of the DK240 480 If the user attempts to use inactive keys while in the MANUAL mode a high pitched inactive key tone will result Note All of the following commands must be executed from the AUTO mode GOTO The user can change the A wavelength by entering a value for a new wavelength and then pressing enter This command changes the grating angle which in turn changes the wavelength at the exit slit Use the GOTO command to instruct the DK240 480 to find a discrete wavelength The values of wavelength are grating dependent Once the key is pre
24. K Murty Theory and Principles of Monochromators Spectrometers and Spectrographs Optical Engineering Vol 13 No 1 Jan 1974 Properties of Spectrometers The four important specifications in selecting a spectrometer are 1 Wavelength resolution the ability of the instrument to differentiate between different wavelength of light 2 Through put the percentage of light that can be sent from a light source through the spectrometer 3 Spectral purity the ratio of the inband light passed by the spectrometer to the transmitted light that falls outside the selected spectral band 4 Price wavelength resolution transmission effeciency and spectral purity can vary dramatically between instruments as the size type quality and design of the optical system differ The relative importance of these specifications depends upon the application A tradeoff can be found between wavelength resolution and price by selecting an instrument with a focal length between 1 8 meter and 2 meter Or a double monochromator offers unbeatable spectral purity Wavelength resolution and its relatives The resolution of a spectrometer is classically defined as the wavelength separation AA between two ideal monochromatic spectral lines of equal intensity when their half maximum intensities overlap since the spectral lines are monochromatic their line shape comes from the instrument This is approximately equivalent to saying that the resolution is the full width
25. SLIT ADJ allows the user to adjust the continuously variable entrance exit slits The power up default slit width is 50 microns This width may be changed to any value between 10 and 3000 microns in the SLIT ADJ routine Depending on the number of times SLIT ADJ is pressed the display will read Press once changes both slits Press twice changes each slit independently SLIT WIDTH xxxx SLIT ADJ NEW WIDTH u 1 ENT SLT 2 EXIT SLT DK242 only SLIT ADJ 1 ENT SLIT 2 EXIT SLT 3 MID SLT Press three times to reset slits Press four times to change bandwidth SLIT RESET 0 ALL BANDWIDTH xxxxnm 1 ENTRANCE 2 EXIT NEW WIDTH nm Pressing will cancel any SLIT ADJ routine and return to the Ready screen Bandwidth will be discussed under CSR Mode SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Operation For independent adjustment of the entrance or exit slit pressing 1 or 2 will display ENT EXITSW 0050 NEW WIDTH u The desired slit width is entered and the entrance exit slit will adjust to the new setting The slit width on the READY screen will always reflect the exit slit setting TEST Initiates an internal diagnostic routine and resets the monochromator Similar to RESET Pressing the TEST function will initiate an internal diagnostic routine in the DK240 480 The display will read ENTER 1 for TEST
26. XXX gt YYY is the model number of the monochromator 240 242 480 XXXXX is the five digit serial number of the monochromator After sending the Echo byte of the TEST command the monochromator will output the TEST status byte The monochromator will perform a reset operation after any of the following commands are sent GRTSEL GCAL S1CAL S2CAL TEST CLEAR or RESET SH Spectral Products 1 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Appendix A Wavelength Ranges A Wavelength Ranges The DK240 480 is restricted to angles between 0 and 70 degrees The upper restriction is imposed because the grating is almost edge on to the incident beam beyond this angle From these restrictions one may use the grating equations to calculate the valid ranges and step sizes for any particular grating The table below lists the maximum wavelength for each grating set in the DK240 480 s software UPPER WAVELENGTH SCAN LIMIT AND MAXIMUM WAVELENGTH INCREMENTS PER ANGULAR STEP FOR DIFFERENT GRATINGS Lower wavelength scan limit is zero Grating Upper limit Grv mm nm 3600 500 2400 750 1800 1000 1200 1500 600 3000 300 6000 150 12000 75 24000 Diffraction Limit to Resolution The grating used in a DK240 480 is a reflective surface with a series of vertical parallel grooves Collimated light is directed toward the grating which in turn
27. all 1 if the specifier was too large Bit 4 0ifscan is negative going GOTO and SCAN only 1 if scan is positive going GOTO and SCAN only Bit 3 Onotused Bit 2 0 if monochromator is not in CSR mode 1 if monochromator is currently in CSR mode Bit 1 Onot used Bit 0 1 if motor movement in negative orders for ZERO operation only 0 if motor movement in positive order for ZERO operation only SH Spectral Products m 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Appendix D NovRam Program D Novram Program Calibration Procedures These commands are Read from Novram and Write to Novram There are 128 memory locations in the Novram and their addresses are from 0 to 127 Table on page 34 gives the address and the meaning in the Novram memory READ FROM NOVRAM These commands read a word 0 to 65535 to a Novram address 1 to 64 indicated by address byte To DK240 480 From DK240 480 To DK240 480 From DK240 480 DK240 480 Action Byte gt From DK240 480 From DK240 480 56 p 56 p Address Byte Data High Byte gt lt Data Low Byte No immediate action The word read from the Novram address is 256 lt High Byte gt lt Low Status Byte gt lt 24 gt p Data Byte contains a returned value and Address Byte is 0 through 127 WRITE TO NOVRAM These commands write a word 0 to 65535 to a Novram address 1 to 64 indicated by address b
28. ated here as they apply to Spectral Products spectrometers Spectral Products dispersive grating instruments come in two forms monochromators that select one wavelength and spectrographs that output a range of wavelengths generally for use with an array detector Both share the same optical concept they are one to one imaging systems in which one image of the entrance slit appears at the exit for each wavelength passed through the instrument Figure shows the optical elements of a typical monochromator Light enters through an entrance slit and is made into a nearly collimated beam by the collimating mirror The light strikes a diffraction grating which then disperses different wavelengths at different angles in the plane of incidence The focusing mirror collects the light from the grating over a range of angles and therefore from a range of wavelengths and images the light to distinct positions near the exit slit The physical position of the image depends on its angle on the camera mirror and the angle depends upon its wavelength Exit slit Focusing mirror Entrance slit J Figurel 1 A typical monochromator Diffraction S Collimating grating mirror During Monochromator scanning the intensity of light that passes the exit slit waxes and wanes as the images of the entrance slit move across see figure 3 1 The intensity at any time is the convolution of the intensity profile of the entrance slit image with th
29. ater Imagine a source that sends two monochromatic lines into a monochromator If the wavelengths are sufficiently different the two monochromatic slit images will not overlap at the exit slit However the finite width of the slits allows the possibility of overlap for some wavelength difference That is the slit width limits the ability to resolve two closely spaced wavelengths Wider monochromator entrance slits allow more light to enter into the instrument Narrower slits allow for better resolution between wavelengths This is one of the basic trade offs in the use of monochromators The wavelength that is passed by the monochromator lambda is described by the grating equation that was presented earlier 2 d COS SIN q 1 nm n or in wavenumbers s em n 0 5 COS N CSC q where d is the grating groove spacing in meters N is the number of grooves per centimeter is the Ebert angle This is a fixed angle determined by the positions of the grating the collimating mirror the camera mirror and is approximately 18 degrees for the DK240 q is the angle of grating rotation measured from the point at which white light is specularly reflected through the instrument Note that 70 is the maximum grating angle n is the order of diffraction Typically for light incident normally to a grating some of the light will be reflected zero order some will be diffracted to the
30. ber of motor steps of Slot 2 10 Number of motor steps of Slot 3 11 Grating 1 Blaze 12 Grating 2 Blaze 13 Grating 3 Blaze 14 Zero Offset of Machine 1 Grating 1 15 Zero Offset of Machine 1 Grating 2 16 Zero Offset of Machine 1 Grating 3 17 Zero Offset of Machine 2 Grating 1 18 Zero Offset of Machine 2 Grating 2 19 Zero Offset of Machine 2 Grating 3 20 Grating 1 Calibration High byte 21 Grating 1 Calibration Low byte 22 Grating 2 Calibration High byte 23 Grating 2 Calibration Low byte 24 Grating 3 Calibration High byte 25 Grating 3 Calibration Low byte 26 Entrance Slit Offset 27 Exit Slit Offset 28 Middle Slit Offset for DK242 only 29 High byte of gratings Low byte Bit 0 0 Full step 1 Micro step 1 Bit 1 0 1 machine 1 2 machine 2 Bit 2 0 no OMA 1 OMA 4 Bit 3 0 no CSR 1 CSR 8 Bit 4 0 no GPIB 1 BPIB 16 Bit 5 0 Unilateral 1 Bilateral 32 30 Model Number 31 Grating 1 groove mm 32 Grating 2 groove mm 33 Grating 3 groove mm 34 Machine 2 Slot 1 35 Machine 2 Slot 2 36 Machine 2 Slot 3 37 Hi byte notused Low byte subtractive 38 Reserved 39 Reserved 40 Reserved 41 Reserved SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 38 key A Spectral Products Appendix E Constant Spectral Resolution E Constant Spectral Resolution CSR Theory The CSR mode allows the DK240 480 to vary the slit width throughout
31. bration number This calibration number is not a count of motor steps or physical location but a scaling factor used as a multiplier throughout the range of grating motion Therefore the monochromator takes the ideal number of motor steps if the unit were optically and geometrically perfect and scales it by the calibration factor Each grating in a multiple grating monochromator has it s own zero and calibration numbers compensating for mechanical or optical variations as the gratings are changed Sources of error The wavelength appearing at the exit slit of a Czerny Turner monochromator the design used in all Spectral Products monochromators is given by the following equation A 2cos o 2 sin 8 N K where 4 Ebert angle 18 7 for a DK240 9 2 for a DK480 25 4 for a CM110 8 Grating rotation from Onm deg N Groove density g mm K Diffraction order Any of the above terms with the exception of Kan integer may be in error The Ebert angle that is the angle subtended at the grating surface by the central rays from the collimating and focusing mirrors will vary from unit to unit The mirrors may not be ground to precisely the same focal length or may be mounted slightly off center either of which will shift K slightly Similarly the groove density of the grating may not be ideal Gratings cut from the same master will be very close to one another but may differ by some percentage from the stated value Both of the above
32. ction From DK240 480 lt 24 gt SH Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 oS Spectral Products Operation SLEW UP Slews the grating towards the longer wavelength until the DK receives a 24 or reaches the limit of the grating operation To DK240 480 From DK240 480 DK240 480 Action To DK240 480 From DK240 480 From DK240 480 SLEW DOWN lt 8 gt p lt 8 gt p Slews until 24 received or limit is reached lt 24 gt p lt Status Byte gt lt 24 gt p Slews the grating towards the shorter wavelength until the DK receives a 24 or reaches the limit of the grating operation To DK240 480 From DK240 480 DK240 480 Action To DK240 480 From DK240 480 From DK240 480 SLIT lt 2 gt p lt 2 gt p Slews until 24 received or limit is reached lt 24 gt p lt Status Byte gt lt 24 gt p Returns the current four byte six byte for DK242 slit width First two bytes are high and low byte of the entrance slit width in microns Second two bytes are the high and low byte of the exit slit width For DK242 the last two bytes are for middle slit width To DK240 480 From DK240 480 From DK240 480 DK240 480 Action From DK240 480 SLTADJ lt 30 gt p lt 30 gt p lt 4 or 6 Bytes gt lt Status Byte gt No action lt 24 gt p Adjusts all slits to a given width To DK240 480 From DK240 480 To DK240 480 From DK240 480 DK240 480 Ac
33. ctory calibration values for the grating and slits This command also executes a reset which returns the grating to home position To DK240 480 lt 25 gt p From DK240 480 x255p From DK240 480 Status Byte gt DK240 480 Action Reset monochromator From DK240 480 lt 24 gt p CSR This command sets monochromator to Constant Spectral Resolution mode The slit width will vary throughout a scan This is useful for example where measurement of a constant interval of frequency is desired spectral power distribution measurements To DK240 480 lt 28 gt p From DK240 480 285 p To DK240 480 High Byte gt Low Byte gt From DK240 480 Status Byte gt DK240 480 Action Set mono to CSR mode From DK240 480 lt 24 gt p Bandpass value HighByte 256 LowByte in hundreth s of nanometers See Appendix F page 36 Constant Spectral Resolution ECHO The ECHO command is used to verify communications with the DK240 480 To DK240 480 LT p From DK240 480 27 p DK240 480 Action No action GCAL This command allows recalibration of the monochromator positioning scale factor and should be used immediately after using the ZERO command see page 15 The monochromator should be set to the peak of a known spectral line then the position of that line is input using the CALIBRATE command CAUTION Use of this command will erase factory settings To DK240 480 lt 18 gt p From DK240 480 185 p To DK240 480 High Byte gt
34. ctrometer that has been set to a wavelength given to return to the original wavelength after the wavelength setting has been changed This is a measure of the mechanics of the wavelength drive and the over all stability of the instrument Wavelength accuracy is the difference between the spectrometer s set wavelength and the true wavelength It is not meaningful to apply a wavelength accuracy to a spectrograph because a wide band of wavelengths exists onto the detector array in a spectrograph In monochromators wavelength accuracy must be checked against known spectral line wavelengths SP checks its monochromators at ten wavelengths across the spectral region SH Spectral Products kii 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 kay A Spectral Products Appendix I Theory Etendue Spectral Energy Density and Throughput The percentage of light that can be sent from a light source through a spectrometer would be a desirable measure of its throughput Unfortunately the properties of sources vary so much that this measure would not provide a useful standard Instead two separate specifications are useful etendue a measure of the degree of coupling that can be achieved and transmission efficiency a measure of how much of the input light exits the monochromator The etendue of an instrument is the product of an instruments physical aperture cm and its angular aperture steridians For a source of a
35. e transmission profile of the exit slit Figure I 2 illustrates collection of a spectrum with a spectrograph and an array detector In this case the array detector elements see a signal that is proportional to the amount of the entrance slit image that falls on the element SH Spectral Products ki 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Appendix I Theory os 2 Intensity 9 6 Lo 0 4 tt cei 0 0 F RETER A ETILI AA NE 2 4 6 8 10 12 14 16 18 20 Pixel number Pixel 0 Array detector Pixel 120 Entrance slit Figure I 2 Array detection in a spectrograph and the resulting spectrum Real sources are polychromatic not monochromatic For each wavelength present in the source an image of the entrance slit appears at slightly different position near the exit The relationship between wavelength and position is referred to as the reciprocal linear dispersion RLD of the spectrometer often referred to as just dispersion and expressed in units of nanometer per millimeter The magnitude of the dispersion depends upon the wavelength the focal length of the focusing mirror and the grating The intensity of polychromatic light passed by the monochromator is a complicated convolution of the intensity profile of the entrance slit image the dispersion of the spectrometer the spherical profile of the source and the transmission profile of the exit slit Most
36. ears the selected grating is ready for use To view the Grating I D BLAZE press the OPTIONS key followed by the 3 key then press the 2 key The grating identifier is now displayed GRT N BLAZE xxxnm RULING yyyy g mm Press any key to return to the READY screen SH Spectral Products A 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lym A Spectral Products Operation Serial Number Pressing the OPTIONS key twice displays the following message on the control module display SERIAL NUMBER XXXXX DIGIKROM YYY XXXXX is the five digit serial number of the monochromator YYY is the model number of the monochromator Press any key to return to the READY screen ENTER STOP Press the ENTER STOP key after every command to carry out that action RESET Resets the grating turret to the home position when pressed simultaneously with the arrow key lt Pressing the RESET and the lt key simultaneously will cause the machine to perform a hardware reset The READY screen will be displayed after the hardware reset has been completed FILTER This option is enabled when a SP filter wheel is attached The Filter option is described in detail in the Filter operations appendix which is included with the purchase of this option The Filter option allows you to rotate the multiple filter wheel assembly so that the selected filter will be placed in the monochromator beam path You may select any one of up t
37. edures failure to follow operating instructions unauthorized modifications and natural disasters are not covered under this warranty The Digikrom DK240 480 does not contain any user serviceable parts Removing its cover without explicit written permission from Spectral Products will void any written or implicit warranty SP reserves the right without prior or further notice to make changes to any of its products described or referred to herein to improve reliability function or design SP accepts no liability for incidental or consequential damages arising from the use of this software SP does not recommend the use of its components or software products in life support applications wherein a malfunction or failure of the product may directly threaten life or result in injury SP does not recommend that this product be used on the same power line as other equipment with high current draw requirements SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Sm Spectral Products Introduction 1 3 Copyrights Spectral Products maintains the copyright on this material but grants the customer rights to use or to modify the software described herein without obtaining Spectral Products permission and without the requirement to reference Spectral Products as the source of the material LabVIEW is a registered trademark of National Instruments Windows Microsoft Visual Ba
38. eflectance of most materials at grazing incidence In Spectral Products spectrometers baffles are treated as if they were mirrors They are used to direct stray light out of the beam path Higher Order Diffraction Higher order diffraction is an inescapable source of stray light in grating based spectrometers The grating equation N lambda d sin i sin r Allows not only first order diffraction of wavelength lambda but coincident diffraction of wavelengths lambda 2 lambda 3 lambda 4 Depending upon the blaze wavelength of the grating the efficiency for diffraction of these higher orders may actually be greater than the first order diffraction efficiency The only way to eliminate these shorter wavelengths is with a filter Fortunately long pass filters are easily obtained Spectral Products offers a series of filters that have been especially selected to suppress higher order diffraction SH Spectral Products n 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key Spectral Products Appendix I Theory Ghosts Ghosts are spurious spectral lines that originate in periodic irregularities in the diffraction grating For a 1200 1 mm grating for example a 01 spurious modulation of the groove profile at 1000 1 mm would produce ghost lines Those ghost lines would have a spacing of about lambda 1 1 1 2 from each spectral line at wavelength lambda Ghosts were originally observed in spectrom
39. ess is complete If your DK242 was set up in subtractive dispersion mode you may now change it back to subtractive mode for calibration If using the Novram utility address 37 should read 65529 To calibrate the DK242 GOTO a known spectral line and manually step the monochromator for proper throughput It may be necessary to open one of the slits to achieve this Typically for additive dispersion the middle slit is wider than the entrance and exit slits and in subtractive dispersion mode the exit slit is kept wider than the entrance and middle slits Once the proper output is obtained issue the CALIBRATE command The DK242 will once again perform a reset routine Replace the baffle and covers SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lym A Spectral Products Appendix H Serial Connections P1 O O O O O o O P2 O O O O O O To DK cae To O Computer O O 2 O O O O 1 DB9 Mal O Connector DB25 Female Connector DB Male Fig I 2 DK To PC 25 Pin Serial Port 57 Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Appendix I Theory I Basics of Optical Spectrometers NOTE TO READERS The basics of optical spectrometers are familiar to most readers of this manual However terminology and interpretations of instrument characteristics vary somewhat and these basics are repe
40. eters because they used ruled gratings manufactured on mechanical ruling machines that had intrinsic periodic errors in their mechanisms Modern interferometrically controlled ruling machines produce gratings that are free of such errors Holographic gratings can also exhibit ghosts some with intensities exceeding conventionally ruled gratings These holographic ghosts originate in extraneous reflections during the hologram exposure Scatter Scatter in a spectrometer is the primary source of diffuse background Scatter does not originate in reflections from walls or other non optical objects within the spectrometer The probability of such light exiting the spectrometer is low Scatter is diffuse reflection at the optical surfaces the result of surface roughness scratches and digs Scatter from the optical surfaces is important because it is most intense at low angles This low angle scatter has a high probability of reaching the detector Spectral Products has extensive experience in producing low scatter laser optics with scratch and dig of 10 5 or better All of this experience has been applied to the optics of Spectral Products spectrometers SH Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908
41. ey The bandwidth should be selected from the allowed bandpass values listed below If an invalid bandwidth has been entered a beep will sound and the display will not change If a valid bandwidth has been selected the slit widths will be automatically adjusted and the display will return to the READY screen When the CSR mode has been selected the character for current grating number at the top right corner of the READY screen will be displayed in reverse video white on black To escape from the CSR display without entering a value press the back arrow key lt SH Spectral Products ii 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Appendix E Constant Spectral Resolution Specifications The allowed bandpass resolution values in the CSR mode are given below With uniform grating illumination and effective slit widths determined only by the physical slits the actual bandpass values will be within 9 of the nominal value Grating lines mm Allowed Bandpass Values nanometers 2400 1 50 0 75 0 37 0 18 1200 3 00 1 50 0 75 0 37 600 6 00 3 00 1 50 0 75 300 12 0 6 00 3 00 1 50 150 24 0 12 0 6 00 3 00 75 48 0 24 0 12 0 6 00 The instrument can be removed from the CSR mode in the following five ways 1 By selecting a specific slit setting By selecting a new grating By resetting recalibrating or clearing the instrument
42. for the FWHM at moderate to wide equal width slits Optical aberrations diffraction scanning method pixel width slit height uniformity of illumination and the like are negligible in this regime The bandwidth then becomes the dispersion times the slit width Bandwidth Spectrograph Spectral Products uses the term Bandwidth to distinguish between the narrow band selected by the monochromator and the wide spectrum output by a spectrograph When coupled to an array detector the bandwidth designates the wavelength range thrown across the entire array Dispersion The reciprocal linear dispersion of a spectrometer can be found the following Leon Radziemski Calculation of dispersion for a plane grating in a Czerny Turner mount a comment Applied Optics Vol 20 No 11 1 June 1981 AA d cos r Ax nf where r is the diffraction angle x is the lateral distance along the focal plane n is the order and fthe focal length of the focusing mirror Reciprocal linear dispersion is not a constant it varies with wavelength and can exceed a factor of two over the useful spectral range Wavelength Precision Reproducibility and Accuracy Wavelength precision is the gradation on the scale that the spectrometer uses in determining wavelength DK series monochromators and spectrographs employ a microstepping grating drive that gives a wavelength precision of 01nm per step with a 1200 I mm grating Wavelength reproducibility is the ability of a spe
43. he hex value into three bytes 2710 base 16 gt 00 27 10 Hi Mid Lo Step 4 Convert each byte to its decimal equivalent Hibyte 00 base 16 gt 00 base 10 Midbyte 27 base 16 gt 39 base 10 Lowbyte 10 base 16 gt 16 base 10 Step 5 Send the command The specifiers are 0 39 and 16 Method B Note All the following numbers are given in decimals Step 2 Divide by 65536 and round down to the nearest whole number EX 1000 65536 0 01526 rounds to 0 Hibyte Step 3 Calculate middle byte EX 10000 65536 x Hibyte 10000 0 10000 10000 256 39 0625 Truncates to 39 Middle byte Step 4 Adjust the remainder EX 0 0625 x 256 16 Lowbyte Step 5 Send the command The specifiers are 0 39 and 16 4 SH Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Appendix B Encoding Decoding Data Bytes DECODING DATA BYTES The desired command is QUERY POSITION The QUERY POSITION command returns two bytes indicating the current wavelength in the form lt HIBYTE gt gt lt MIDBYTE gt lt LOWBYTE gt To be useful to the user the two bytes must be converted back to a single decimal number As before we can do this by either method A or method B by essentially reversing the above procedures For this example the QUERY POSITION command returns the ordered pair 5 4 106 Hibyte Lowbyte respectively as the current wavelength For thi
44. ing Data Bytes B Encoding Decoding Data Bytes Many computer based commands RS 232 both send and receive information in the form of multi byte specifiers For a number given in decimal form such as base 10 to be sent to the monochromator the number must first be broken down into hexadecimal bytes 8 bits Then each byte is converted into a decimal value This decimal value is transmitted as a ASCII character to the communication device Then the monochromator translates the characters into the form necessary to perform the operation Conversely the monochromator sends the data back in decimal characters Each is a byte long and the computer application must convert these separate bytes back to a useful decimal value ENCODING DATA BYTES The desired command is GOTO 100 nm The GOTO command in RS 232 is specified as lt 16 gt lt HIBYTE gt gt lt MIDBY TE gt lt LOWBYTE gt where the units for the two byte specifier are determined by the current UNITS selected For this example the units are in Angstroms Step 1 Convert the desired specifier to proper units 100 nm 10000 hundredths of nm NOTE The following steps will be shown two ways A with conversions performed by a unspecified algorithm for example using a calculator with decimal hex conversion capability and B using a numeric algorithm that is more suitable for computers Method A Step 2 Convert to Hexadecimal 1000 base 10 2710 base 16 Step 3 Break t
45. l program with source is included A LabVIEW Driver is available upon request Power UL listed 110 220 V power pack meets or exceeds UL1950 CSA 1402C and IEC 950 Interface RS 232 standard Warranty One year from delivery date CE marked SH Spectral Products o 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lim A Spectral Products Operation 2 4 DK Series Specifications 2 4 1 Wavelength Accuracy Grating g mm DK240 242 DK480 3600 lnm Inm 2400 2nm 2nm 1200 3nm 3nm 600 6nm 6nm 300 1 2nm 1 2nm 150 2 4nm 2 4nm 75 4 8nm 4 8nm 50 7 2nm 7 2nm 2 4 4 Slits2 4 2 Resolution Grating g mm DK240 DK242 DK480 3600 04nm 04nm 02nm 2400 08nm 08nm 03nm 1200 15nm 15nm 06nm 600 2nm 2nm 12nm 300 4nm 4nm 24nm 150 8nm 8nm 48nm 75 1 6nm 1 6nm lnm 50 2 4nm 2 4nm 1 8nm 2 4 3 Wavelength Precision Grating g mm Micro stepped 3600 0lnm 2400 0lnm 1200 0lnm 600 02nm 300 04nm 150 08nm 75 16nm 50 24nm 2 4 4 Slits Type Increment Minimum Maximum Unilateral lu 3000u Bilateral lu 5000u GA Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lym A Spectral Products Operation 2 5 Software DK240 480 Demo Software Windows DK series monochromator demonstration software is written in Microsoft Visual Basic 16 bit Ver 4 0 for Windows and will run on Windows 3 11 95 98 2000 and NT 4 0 The demons
46. le mirror n is the number of mirrors Rg is the diffraction efficiency of the grating Mirror reflectance is typically 0 92 for a protected aluminum mirror In a four mirror system about 70 is transmitted by the mirrors SP offers custom broadband high reflectance coatings that can boost this efficiency to almost 95 in a four mirror system over about a wavelength octave Grating diffraction is quite complicated it is both wavelength and polarization dependent Grating diffraction efficiency for a ruled grating typically reaches 90 at the blaze wavelength falling off to 20 at 0 6 lambda blaze and 1 5 lambda blaze Holographic gratings typically have a flatter 30 efficiency Careful selection of gratings to match the spectral regions of interest will allow good transmission efficiency at any wavelength We can get a measure of total spectrometer through put per nanometer by multiplying the spectral energy density by the transmission efficiency The result is H Sh f Wg A Rm n Rg SH Spectral Products a 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Appendix I Theory The F f Misconception F is the measure of the acceptance angle of an optical instrument and is generally defined at the ratio of diameter to focal length For years F has been promoted as the measure of monochromator throughput However as previously discussed grating size is the domi
47. n your NOVRAM s memory Using a discrete light source such as a HeNe laser or a Hg pen lamp illuminate the entrance slit Make sure the light source is aligned perpendicular to the entrance slit Using SLITADJ set both slits entrance and exit to S0u Use an appropriate detector for determining maximum intensity Using GOTO set A to the new wavelength Press Enter If the new wavelength is not correct enter into MANUAL mode In MANUAL mode 1 single step below current A 2 scan below current A 3 slew below current 7 single step above current A 8 scan step above current 9 slew step above current A It is best to single step while observing detector for maximum peak intensity Press MANUAL again to get back to the Ready screen To calibrate this new wavelength Press OPTIONS until CALIBRATION appears Press 1 Calibrate Press 1 Cal Grating Press Enter This states machine is aligned Type new wavelength Press Enter Note The arrow key will allow you to exit this procedure at any time except at step 12 SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lim A Spectral Products Operation 3 2 5 Slit Calibration Pressing the keys OPTIONS then 2 then 3 will initiate slit calibration and will produce similar displays and invoke the slit calibration routines Please consult SP before proceeding As with the grating calibration the
48. nant factor in throughput For example a F 4 monochromator with a 30 mm grating will have 44 more throughput than a F 2 5 monochromator with only a 25mm grating Similarly a F 4 monochromator with a 68mm grating will have 85 more through put than a F 3 monochromator with a 50mm grating However F is a useful concept in judging optimum coupling between spectrometers and sources or detectors When F s are matched the full aperture of the spectrometer will be utilized SH Spectral Products aR 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lm A Spectral Products Appendix I Theory Stray Light Stray light is all out of band light transmitted by a spectrometer Because the spectral profile of the source and the spectral sensitivity of the detector may enhance or under estimate the measured spectral purity two distinct methods of stray light measurement have evolved The ASTM has published a filter method for measuring stray light in spectrometers This method uses an incandescent lamp together with long and short pass blocking filters This is useful for measuring the contribution of stray light originating far from the bandpass region when using a continuum source Instruments SA introduced another method in the 1960s that is particularly relevant for laser spectroscopy Their measure of stray light is the inverse ratio of light at the peak of a 632 8nm laser source to the light measured at 5 ba
49. ndpasses from the peak This method measures the contribution of stray light originating near the bandpass region when using a line source The following discussion reviews most of the sources of stray light in spectrometers Rediffracted Light Rediffracted light originates when a secondary order of diffracted light goes from the grating back to the collimating mirror The light may then be reflected back to the grating where it is rediffracted Because of the double bounce on the collimating mirror the rediffracted light arrives at the exit slit unfocused Typically it will be 0 1 of the ordinary signal A discussion of rediffracted light is given in Mittledorf and Landon Rediffracted light usually appears as a long wavelength spectral impurity in short wavelength light Eliminating rediffracted light is a matter of design geometry Secondary Sources Secondary sources are sources of reflection within the spectrometer that direct stray light back into the main beam path A typical example is a well intentioned but troublesome baffle placed nearly parallel to the beam path Grazing incidence reflection off such a baffle will send light close enough to the correct beam path to end up as stray light at the exit Stray light from secondary sources generally appears as a broad flat topped band in a spectral scan Its intensity will be very sensitive to the illumination conditions Blackening the baffle does not reduce the effect because of the strong r
50. nge of the physical slit width will have no effect Similarly if the exit slit is imaged on a detector and if that detector is smaller than the slit image changing the physical slit width will again have no effect 2 The resolution of a monochromator depends in part on uniform illumination of the grating If uniform illumination is not maintained as the slits are widened then constant spectral resolution may not be obtained 3 The slit settings are not continuously variable the changes in the slit widths that are used to maintain constant spectral resolution may result in observable steps in the output intensity To restrict this effect the smallest slit width that is used in the CSR mode is 106 microns or 1 of the slit width increment With the exception of slit setting operation in the CSR mode leaves the other functions unchanged When the monochromator is positioned using GOTO or scanned using SCAN the slit widths will be continuously and automatically adjusted to provide constant bandwidth The CSR mode is selected by pressing the SLIT ADJ key four times The display will respond as shown below BANDWIDTH xx xxnm NEW WIDTH nm If the monochromator is currently in the CSR mode then XX XX will be the current bandwidth If the monochromator is not in the CSR mode then XX XX will be the maximum allowed bandwidth for the current grating The CSR bandwidth is entered at the prompt using the numeric keys then pressing the ENTER STOP k
51. o home position From DK240 480 lt 24 gt p SCAN This command scans the monochromator between the present position and a alternate specified wavelength at a rate determined by the SPEED command Valid values of position are grating dependent To DK240 480 lt 12 gt p From DK240 480 IZ p To DK240 480 High Byte Mid Byte gt Low Byte gt From DK240 480 Status Byte gt DK240 480 Action Scans the grating to the desired wavelength From DK240 480 lt 24 gt p SCAN UP Scans faster than slewing the grating towards the longer wavelength until the DK receives a 24 or reaches the limit of the grating operation To DK240 480 lt 9 gt p From DK240 480 lt 9 gt p DK240 480 Action Slews until 24 received or limit is reached To DK240 480 lt 24 gt p From DK240 480 Status Byte gt From DK240 480 lt 24 gt p SCANDOWN Scans faster than slewing the grating towards the shorter wavelength until the DK receives a 24 or reaches the limit of the grating operation To DK240 480 lt 3 gt p From DK240 480 lt 3 gt p DK240 480 Action Slews until 24 received or limit is reached To DK240 480 lt 24 gt p From DK240 480 Status Byte gt From DK240 480 4245 p SERIAL Returns the 5 digit serial number of the monochromator To DK240 480 lt 33 gt p From DK240 480 x4335p lt 1 Digit gt lt 2 Digit gt lt 3 Digit gt lt 4 Digit gt lt 5 Digi From DK240 480 Status Byte gt DK240 480 Action No a
52. o six filter positions Filters are specified by the user at the time of purchase 3 2 2 Error Screens INVALID VALUE ENTRY Whenever a value is entered that is out of the grating range the following screen appears VALUE TOO LARGE HIT ANY KEY TO CONT When an invalid value is entered for grating SCAN SPEED the following screen appears INVALID VALUE HIT ANY KEY TO CONT SH Spectral Products iu 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lim A Spectral Products Operation 3 2 3 CALIBRATING ZERO WITH A HANDHELD CONTROLLER ex oba Wa x Calibrating zero will erase the value previously programmed into your NOVRAM s memory Using a white light source illuminate the entrance slit Make sure the light source is aligned perpendicular to the entrance slit Using SLITADJ set both slits to 50u Press GOTO and set A 0 Look through exit slit You should see an illuminated white light source If necessary you may have to reset the Zero location using the MANUAL command Press MANUAL Pressing 1 will single step the grating below zero Pressing 7 will single step grating above zero Step up and down until the brightest light is seen at the exit slit Press MANUAL to get back to the Ready screen To re zero press OPTIONS then 1 calibrate then 2 zero 3 2 4 CALIBRATING AT A WAVELENGTH WITH A HANDHELD CONTROLLER ox ipo to Recalibration will erase the values previously programmed i
53. ptical Diagram of DK240 480 41 Optical Diagram of DK242 41 G DK242 Calibration 43 H Serial Connections 44 I Theory 45 Sm Spectral Products Introduction Introduction 1 1 Mission Statement Our mission is to provide our customers with reliable products on time and at a fair price We are continually striving to maintain the highest standards by assuring defect free products and by providing prompt and courteous customer service The staff at Spectral Products SP will be happy to answer any questions about our products and our services For immediate assistance please contact the Spectral Products directly at 505 296 9541 by fax 505 998 4746 or by e mail at instruments cvilaser com 1 2 Warranty This product is warranted to be free of defects in materials and workmanship for one year from date of purchase This manual and the software it describes are provided free of charge as a service to the customer The software is intended to be used as a tool for development and as an example of one possible method of code implementation It is not intended to be a user application Any software associated with this product is provided as is with no warranty expressed or implied While it is Spectral Products intent to provide error free development tools no guarantee is made regarding either the accuracy or usefulness of this material Failures or damages resulting from lack of operator attention to proper proc
54. r spectral line which gives the best fit to the line set being examined Automated scans then check for repeatability throughout the line set recalibrating the unit as necessary A technician who writes the calibration into non volatile RAM then checks final calibration Acceptable errors for various grating groove densities are listed below Numbers given are for the DK series for the CM series the numbers are somewhat higher than those shown due to its smaller worm wheel and gear ratio Density g mm Accuracy nm Repeatability nm 3600 0 10 0 03 2400 0 15 0 06 1200 0 30 0 10 600 0 60 0 20 300 1 20 0 40 150 2 40 0 80 75 4 80 1 60 50 7 20 2 40 Note that the acceptable error varies inversely with the groove density This is because it is actually the same angular error of grating position Further these numbers are generalized to the middle of the grating range about 30 from the zero order point As can be seen from the grating equation the output wavelength is not a linear function of the grating angle therefore the same absolute error in grating position will produce a varying amount of wavelength error across the range of the grating Operation 3 1 Command Summary The subscript p indicates the decimal value of the byte is listed SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Operation CLEAR This command restores fa
55. roducts Download Software and then the file 8 0114 d exe Once the DK242 is in additive mode remove power from the unit Remove the slit cover plates remove the cover and then remove the top baffle Apply power and set your light source to the entrance slit Once the DK242 has finished it s reset routine instruct it to GOTO zero See if light is moving through the middle slit If it is not you must manually step the MI machine 1 the half closest to the entrance slit grating until the best throughput is achieved This can be done either with the handheld controller MANUAL mode or with the demo software increment decrement Once the zero order is optimized for M1 issue the ZERO command for M1 The monochromator will now perform a reset routine Once reset GOTO zero and check that the light goes through the middle slit If it is not quite optimized repeat the procedure until you get the throughput desired After M1 is properly zeroed instruct the DK242 to GOTO zero Observe the light at the exit slit If the light does not exit the monochromator M2 must be zeroed To zero M2 you must unplug the motor wires from M1 the four or six wires running directly from the motor to a small circuit board on the DK242 end plate then manually step M2 just as you did for M1 above Once the light exits the entire monochromator plug the M1 motor wires back in and issue a ZERO command for M2 Once your light source exits the entire DK242 the zero proc
56. rom DK to computer 4 RTS Clear to Send output from host to DK 5 CTS Request to Send output from DK to host 6 DTR Data Terminal Ready output from DK to host 7 GND Signal Ground common with chassis ground 8 24 Not used 25 5v Receive current loop return The pin assignments above are mapped one to one between the cable connection of a Digikrom and an IBM AT style serial communications port The Digikrom emulates data communication equipment DCE when communicating with a remote computer No crossing of data or handshake lines are necessary The request to send clear lines are used for handshake protocol of control communications The Digikrom DK240 480 is factory configured and the character length number of stop bits and parity cannot be changed Its signal levels and format are the same as those that are specified for the RS 232 The computer must be set to the Digikrom DK240 480 data type and baud rate Character length 8 bits Baud rate 9600 bits sec Stop bits 1 Parity None 5A zo Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lm A Spectral Products Operation Command Clear CSR Echo Gcal Goto Grtid Grtsel Reset Scan Scan Up Scan Down Serial Slew Up Slew Down Slit Reset Slit Sltadj Speed Sspeed Step down Step up Sladj S2adj S3adj S1cal S2cal S3cal Wave Zero Byte Decimal lt 25 gt lt 28 gt lt 27 gt
57. s example the units are in Angstroms Method A Step 1 Convert each byte to its hex equivalent Hibyte 05 base 10 5 base 16 Midbyte 04 base 10 4 base 16 Lowbyte 106 base 10 6A base 16 Step 2 Concatenate the 3 bytes to form one hex number 05 04 6A 05046A base 16 Step 3 Convert the hex number to a decimal 05046A base 16 328810 3288 10 nm Method B Note All of the following numbers are in hundredths of nm Step 1 Use the formula Wavelength A Hibyte x 65536 Midbyte x 256 Lowbyte 5 x 65536 4 x 256 106 328810 hundredths of nm 3288 10nm SH Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lm A Spectral Products Appendix C Status Bytes C Status Bytes Whenever the DK240 480 is given a command it will respond with a status byte that indicates whether the command was accepted Each bit in the status byte has a meaning which is given below When a command is not accepted some of the bits of the status byte will indicate the reason In general if lt Status Byte gt p is smaller than 128 then the command was accepted Bit 7 0 if specifier value acceptable bit 4 active bits 5 6 inactive 1 if specifier value not acceptable bits 5 6 active bit 4 inactive Bit 6 0 if specifier value not equal to present value bit 5 active 1 if specifier value equal to present value bit 5 inactive Bit5 0ifthe specifier was too sm
58. sic and Microsoft Quick Basic are registered trademarks of Microsoft Corporation 1 4 Product Overview The Digikrom DK240 480 are and meter Czerny Tumer type monochromator spectrographs Focal lengths are 240mm and 480mm respectively The grating s of your Digikrom are controlled by a microprocessor driven stepper motor which is coupled to the grating table Thus there is no sine bar drive mechanism in the Digikrom monochromators This design permits a simple rugged mechanism which is less likely to drift out of calibration during extensive use and or rough handling The Digikrom is controlled by a handheld controller direct RS 232 computer control or by using the optional GPIB IEEE 488 interface All necessary protocol and command functions are given in this manual SH Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam A Spectral Products Operation Getting Started 2 1 Verify Shipping Contents The Digikrom 240 480 monochromators do not require removal of any interior shipping restraints NOTE This equipment contains static sensitive devices Handle equipment in a static safe environment until power can be supplied to the unit The following items are shipped with your order of a DK series monochromator Qty Item DK240 480 242 DK24Vxx power supply User s manual Demonstration CD software Al Spectral Products software can be downloaded at
59. speeds will be integer numbers from 1 to 600 x 1200 current grating groove For example with a 600 groove grating valid values are 2 4 8 1200 Speed will be an integer number and is truncated after the calculation SSPEED Returns the current scan speed To DK240 480 lt 21 gt p From DK240 480 215p From DK240 480 lt High Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action No immediate action From DK240 480 lt 24 gt p STEPDOWN Moves the grating one step toward UV To DK240 480 Dp From DK240 480 lt 1 gt p From DK240 480 Status byte DK240 480 Action If valid moves the grating to a shorter wavelength in 1 motor step From DK240 480 lt 24 gt p STEP UP Moves the grating one step toward IR To DK240 480 Tp From DK240 480 lt 7 gt p From DK240 480 Status byte DK240 480 Action If valid moves the grating to a longer wavelength in 1 motor step From DK240 480 lt 24 gt p TEST Performs automatic self diagnosis To DK240 480 lt 17 gt p From DK240 480 lt 17 gt p From DK240 480 Status byte DK240 480 Action Mono initiates self diagnostic routine and will reset after sending lt 24 gt From DK240 480 lt 24 gt p SH Spectral Products i 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 oS Spectral Products Operation WAVE Returns the 3 byte current wavelength setting To DK240 480 lt 29 gt p From DK240
60. ssed the display reads GOTO ENTERA A XXxxx nm In response to this prompt the user may type the desired wavelength value and press ENTER During this part of the operation the display reads GOTO xxxxx RUNNING A yyyyyy nm Once the DK 240 480 finds the specified wavelength the GOTO operation stops and the READY screen appears SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Operation SCAN The user can scan the intensity of light leaving the exit slit over a wavelength range defined as A A The user can scan different ranges of wavelength by entering the values of and A with this command then pressing enter The SCAN key allows the user to scan between a start and an end position specified by the user The START position A may be greater or smaller than the END position Az Valid values of position are grating dependent The scanning speed for the SCAN command is a constant and is determined by the user Once the SCAN key is pressed the display reads SCAN A Ay ENTER A nm Type the starting wavelength and press ENTER The display will then read SCAN xxxxx A ENTER 2 nm Type the ending wavelength and press ENTER The display will then read ENTER NUMBER OF SCAN REPETITIONS Type a number from 1 to 999 Press Enter Ifno number is typed and you press Enter scan will start and complete one repetition If
61. tes are enclosed in the back and forward arrow keys lt gt and separated by commas eg lt OK SC CSR gt lt OK gt Command executed and specifier value acceptable SV Specifier value sent is the same as the current value SVO Specifier value is too small lt SVI gt Specifier value is too big lt SV2 gt Invalid CSR bandwidth value sent lt SCt gt Positive going SCAN or GOTO towards longer wavelengths lt SC gt Negative going SCAN or GOTO towards shorter wavelengths lt CSR gt Monochromator is currently in the CSR mode SPs pectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lim Spectral Products Operation GPIB Commands Query Specifier value definition GOTO XXXXXXX XXXXXXX wavelength unit enter as tenths of angstroms SCAN XXXXXXX GCAL XXXXXXX SSPEED yyyy yyyy scan speed in nm min SICAL ZZZZ ZZZZ slit width in microns S2CAL ZZZZ SLTADJ ZZZZ SLADJ ZZZZ S2ADJ ZZZZ CSR xxxx Xxxx Bandpass value chart on page 37 MANUAL s s step direction 7 positive 1 negative GRTSEL n n Grating number 1 2 or 3 ZERO g g machine number 1 or 2 CLEAR TEST WAVE SLIT IDN ECHO Except for the IDN command all commands operate as defined in Command Summary page 10 When the IDN query is sent the monochromator will return the firmware identifier string lt SP INSTRUMENTS DIGIKROM YYYY XX
62. the tightest of tolerances As an example the DK series use a 64 pitch worm wheel 180 tooth and 2 8125 pitch diameter AGMA Q14 tolerances give a tooth to tooth error tolerance of 0 00014 with a total composite tolerance of 0 00032 Therefore the tooth to tooth angular error is given by A9 sin 0 00014 2 8125 2 0 0057 Total composite error i e from one random tooth to another would be 0 013 so the worm wheel alone can contribute an absolute error of 50 micro steps in a standard DK For a 1200g mm grating around 600nm that error would be about 0 35nm and we are only considering errors introduced by the worm wheel itself Experiments have demonstrated that the motor shaft worm assembly contributes errors much more important in determining the usability of a given grating drive These errors tend to be pseudo sinusoidal cycling every 2 of grating motion and at least as great in amplitude as the maximum wheel error Acceptance criteria Monochromators are aligned and calibrated at Spectral Products by using a HeNe laser to level and align the optics and to give an approximate calibration assuming the laser frequency is within the grating s response range A spectral line source such as an Ar or Hg lamp is then used to fine tune the calibration checking for repeatability and accuracy Typically 8 to 10 known spectral lines are examined for each grating The calibration factor is determined by calibrating to the particula
63. tion From DK240 480 SIADJ 145 p lt 14 gt p lt High Byte gt lt Low Byte gt lt Status byte gt If valid adjusts all slits to the new width lt 24 gt p Adjusts entrance slit to a given width To DK240 480 From DK240 480 To DK240 480 From DK240 480 DK240 480 Action From DK240 480 lt 31 gt p lt 31 gt p lt High Byte gt lt Low Byte gt lt Status byte gt If valid adjusts the entrance slit lt 24 gt p SH Spectral Products Li 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 St Spectral Products S2ADJ Adjusts exit slit to a given width To DK240 480 lt 32 gt p From DK240 480 32 p To DK240 480 High Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action If valid adjusts the exit slit From DK240 480 lt 24 gt p S3ADJ DK242 Only Adjusts middle slit to a given width To DK240 480 lt 34 gt p From DK240 480 lt 34 gt p To DK240 480 lt High Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action If valid adjusts the middle slit From DK240 480 lt 24 gt p Operation SICAL Allows for entrance slit calibration Uses the same procedure as GCAL but with a two byte slit width specifier To DK240 480 lt 22 gt p From DK240 480 22 p To DK240 480 High Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action No immediate action From DK240 480 lt 24 gt p S2CAL Allo
64. to scattering from slit edges and dust or aberrations in the optical elements 5A Spectral Products a 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lam Spectral Products Appendix G DK242 Calibration G DK242 Calibration The DK242 establishes a zero order offset value for each half of the monochromator In other words each grating has its own zero offset Calibration offset is different in that one value is established for each pair of gratings It is very important to have the DK242 zeroed properly to receive a satisfactory output from the monochromator You will need two small hex wrenches 1 16 and 3 32 and a visible light source for this procedure A laser source such as a HeNe works best but it can be done with a white light and atomic line pen lamp l Whether your DK242 was purchased in either ADDITIVE or SUBTRACTIVE dispersion mode it must be in ADDITIVE mode to perform the zero function If your DK242 is subtractive you can change to additive mode any of the following ways a If you have a handheld control module you can change to additive dispersion by pressing OPTIONS the number 4 then enter b If you have a diskette with the SP Novram utilities program on it run that program to access the Program Change values screen Change address 37 to read 65520 c You can access the SP website www cvilaser com to download the Novram software as well Click on Spectral P
65. tration software along with instructions for operation is found on the CD software disk If you are interested in writing custom software that supports the DK240 480 we will be pleased to send this source code upon request If you have any questions about the operation of your monochromator or if you have suggestions please contact us We appreciate your comments and suggestions Spectral Products 200 Dorado Place SE Albuquerque New Mexico 87123 877 208 0245 5A Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lm Spectral Products Operation 2 6 Theory Of Operation The optics of monochromators are designed so that for monochromatic light an image of the entrance slit is formed at the exit slit Scanning the monochromator rotates the grating and moves this image across the exit slit If one were to measure the intensity of the light exiting the monochromator as this scanning occurs one would see that a triangular intensity profile results This is shown in Fig 2 1 Diffraction and other aberrations cause deviations from this ideal situation Because of the physics of diffraction gratings entrance slit images are formed at different angles for different monochromatic wavelengths Therefore rotating the grating also selects a changing wavelength region This is described by the grating equation 2 d COS E SIN q l n This equation will be described in detail l
66. values will affect the calibration of a given instrument but once fixed they remain constant for that particular unit and are accounted for by the calibration factor By far the most critical source of error is the value of 0 Spectral Products monochromators use a worm wheel grating drive driven by a step motor The sources of error in such a system are multiple non linearity of the worm wheel non linearity of the worm step angle errors in the motor eccentricity of any of the shafts or assemblies and any play in any part of the assembly We attempt to ameliorate these errors through such means as 1 Specifying ABEC 7 tolerance level in the bearings 2 Specifying AGMA Q14 tolerance worms and worm wheels 3 Specifying bores to 0 00025 tolerance shaft run outs to 001 4 Utilizing the highest quality step motors and driver electronics available SH Spectral Products a 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 kay A Spectral Products Operation 5 Testing and run in of all assemblies prior to integrating them into a monochromator rejecting and or rebuilding them as necessary 6 Testing in the final unit rejecting and replacing drives that do not meet criteria for accuracy and repeatability The above factors are all an attempt to achieve accuracy on the order of step size resolution of each instrument 0 00025 for the DK series But such accuracy is not theoretically possible even with
67. ws for exit slit calibration Uses the same procedure as GCAL but with a two byte slit width specifier To DK240 480 lt 23 gt p From DK240 480 lt 23 gt p To DK240 480 lt High Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action No immediate action From DK240 480 lt 24 gt p S3CAL DK242 onl Allows for middle slit calibration Uses the same procedure as GCAL but with a two byte slit width specifier To DK240 480 lt 35 gt p From DK240 480 lt 35 gt p To DK240 480 lt High Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action No immediate action From DK240 480 24 p 5A Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Operation SPEED Selects the speed at which the monochromator may scan To DK240 480 lt 13 gt p From DK240 480 lt 13 gt p To DK240 480 lt High Byte gt lt Low Byte gt From DK240 480 Status byte DK240 480 Action No immediate action If a valid value in nm min is selected the SCAN command will thereafter cause the monochromator to move at approximately a speed value of 256 High Byte gt lt Low Byte gt From DK240 480 lt 24 gt p Relevant scan speeds nm minute If grating grooves are greater than or equal to 1200 g mm then the valid values for scan speeds will be from 1 to 600 If grating grooves are less than 1200 g mm then the valid values for scan
68. you enter a number the display will then read ENTER NUMBER OF SECS TO PAUSE Type a number from 1 to 999 Press Enter Ifno number is typed and you press Enter the scan will start completing one repetition If you enter a number the display will then read SCAN A xxxxxnm SCANNING yyyyy After the number is entered the scan will begin When the scan is complete the READY screen will be displayed SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 key A Spectral Products Operation SCAN SPEED This command selects the speed at which the DK240 480 will scan the intensity of light at the exit slit for a given wavelength range The user should refer to Appendix B page 19 for a list of scan speeds that are appropriate for various gratings The SCAN SPEED key allows the user to control the rate at which the wavelength changes Values of speed are grating and units dependent and are given in Appendix E page 34 Once the key is pressed the display reads ENTER 1 SCAN SPEED 2 WRITE TO NOVRAM Caution do not press number 2 This will change factory settings Press 1 and display will read SCAN SPEED xxxxnm m NEW SPEED yyyynm m XXXxX is current scan speed Enter new scan speed and press Enter Display will return to Ready screen and the new speed will be displayed within the screen SS SLIT ADJ This command allows the user to change slit widths The
69. yte WARNING Improper use of this command may corrupt the configuration and calibration information of the To DK240 480 From DK240 480 To DK240 480 DK240 480 Action monochromator See Restore Disk supplied to restore values lt 59 gt p lt 59 gt p Address Byte Data High Byte gt lt Data Low Byte gt lt Checksum Byte gt No immediate action Writes a word 2 bytes to the monochromator s non volatile memory CheckSum Byte Address Byte Data High Byte Data Low Byte The addition is operated in one byte method The Cary bit will truncate if it exists Therefore it is always Checksum lt 255 From DK240 480 From DK240 480 lt Status Byte gt lt 24 gt p CALIBRATION Proper calibration should always be a two step procedure where ZERO is set first followed by calibrating at a specific wavelength as follows SH Spectral Products 200 Dorado Place SE Albuquerque NM 87123 Phone 877 208 0245 Fax 505 298 9908 Lm A Spectral Products Appendix D NovRam Program NOVRAM ADDRESS Address The meaning of the content 1 AAAAH if programmed else random 2 Serial Number 3 Source not used 4 Source 2 not used 5 Source 3 not used 6 Source 4 not used 7 High byte Current source not used Low byte IEEE address 8 Number of motor steps of Slot 1 9 Num

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