6200 rev.D
Contents
1. SOURCE CONTROLS and SOURCE QUERIES Command Control Form Query Form Description Explanation Control Form 58 W SOURce CURRent LEVel DIODe lt wsp gt lt value gt SOURce CURRent LEVel DIODe Write and read the diode current set point lt value lt 152 The units are milliamps This command sets the diode laser current This command always forces the laser into Remote Mode Ifthe value sent is out of range The controller returns Out of Range No other action is taken If the value is in range The diode laser current is changed The controller retums OK Ifthe laser was in Remote Mode The Remote LED is already on The current control DAC is driven to a voltage which produces the requested current within 3 The piezo voltage and the diode temperature are unaffected Explanation Query Form W Ifthe laser wasin Local Mode The Remote LED comes on Control of the laser is given to the DACs The current control DAC is driven to a voltage which produces the requested current within 3 The temperature control DAC and the piezo control DAC are driven to voltages which produce values within 3 of the value they had under front panel potentiometer control The laser isnowin Remote Mode If the laser was in Remote Mode Remote LED is already on The current piezo voltage and diode temperature are unaffected Returns the the last cu2. 59 2 SENSE CURR DIOD gt 59 2 Command Description Explanation Example W SENSe POWer LEVel FRONt Read front facet power Retums the laser output power in milliwatts The value returned is exactly the same as that seen on the front panel of the controller at the time the com mand is executed Note that there are two power readings One is derived from a front facet mea surement and the other from a back facet measurement The front facet power measurement looks at light sampled with a beam splitter at the laser head output The back facet measurement is merely proportional to the opti cal power emitted from the rear facet of the laser gain element It is provided for backward compatibility with 6100 series laser heads or as a diagnostic The output power indicator on the front panel reads 2 6 mW SENS POW FRON gt 2 6 49 50 Command Description Explanation Example W SENSe POWer LEVel REAR Read rear facet power Returns a number proportional to the power emitted from the rear facet of the laser gain element This is provided for backward compatibility with 6100 series laser heads or asa diagnostic Use the front facet power measurement to determine the actual optical power output from the laser SENS POW REAR gt 2 9 Command Description Explanation Example W SENSe TEMPerature LEVel DIODe Read diode temperature Retums th
3. gt EVel AUXiliary Read user analog voltage lt value 0 5 V gt WAVElength Read output wavelength lt value nm gt CURRent LEVel D IODe lt wsp gt lt value gt Write diode current set point TEMPerature LEVel DIODe lt wsp gt lt value gt White diode temperature set point VOLTage LEVel PII EZo lt wsp gt lt value gt Write piezoelectric voltage set point Source Queries SOURce Write retum slew rate set point SOURCE SOURce SOURce SOURce SOURCE SOURce SOURce W WAVElength lt wsp gt lt value MIN MAX gt Write output wavelength set point WAVElength SLEWrate FORWard lt wsp gt lt value gt Write forward slew rate set point WAVElength SLEWrate RETurn lt wsp gt lt value gt LT WAVI LT WAV length STARt lt wsp gt lt value gt Write scan start wavelength set point length STOP lt wsp gt lt value gt Write scan stop wavelength set point CURRent Read diode current set point lt value mA gt LEVel DIODe TEMPerature LEVel DIODe VOLTage I Read diode temperature set point lt value deg C gt EVel PIEZo Read piezoelectric voltage set point lt value 0 100 gt SOURce SOURce SOURce WAVElength lt wsp gt l
4. 82 W
5. Error 14 Error 15 Microprocessor RAM error EPROM revision number mismatch Current board revision wrong Temperature board revision wrong Laser head EEPROM stability error or there is a com patibility conflict between controller and laser head VIII AC Operating Voltages W The Model 6200 Controller can operate at 100 120 220 or 240 VAC at AC frequencies of 47 63 Hz The unit is configured at the factory for the standard AC voltage in the owner s country To select a different operating voltage please refer to Fig 8 pg 80 and follow the directions below 1 2 Disconnect the power cord Open the cover of the power entry module on the rear panel with a small blade screwdriver or similar tool Insert the tool into the voltage selection slot and remove the wheel from theunit Tum the wheel and re insert into the module so the desired voltage is shown Do not attempt to rotate the wheel while it is still in the power entry module the wheel must be removed turned and then re inserted Close the cover Verify the proper voltage is showing through the module s window 79 W The power entry module requires two 5x20 mm slow blow fuses such as Littlefuse s Slo Blo 239 series one for the hot line and the other for the neutral line Replacement fuses should be as follows ACWltage FuseRating Little Fuse 100 VAC 2 0A 239 002 120 VAC 2 0A 239 002 220 VAC 1 6A 239 01 6 240 VAC 1 6A 239 01 6 Fig
6. GPIB card INCLUDE qbdecl bas Clear screen allocate 32 spaces to the string variable buff CLS buff SPACES 32 Find the laser controller at GPIB address 1 CALL IBDEV 0 1 0 T10s 1 nflaser used to specify device in IB function calls EOS character and modes EOI mode of the device I O timeout value 10 sec secondary GPIB address primary GPIB address change if laser is at a different address GPIB board number E Di Clear the controller s GPIB port nflaser is an integer that identifies the laser It was set by IBDEV above we never need to know its value except that it is set to 1 if IBDEV fails to find the device CALL IBCLR nflaser Ask user for a wavelength in nanometers wavelength is a single precision floating point number 775 1 for example INPUT What wavelength would you like nm wavelength 29 W Use IBWRT to send the WAVELENGTH command to the controller Example IBWRT nflaser5 WAVELENGTH 772 0 The STR function converts numbers to strings CALL IBWRT nflaser WAVELENGTH STR wavelength Read the output buffer CALL IBRD nflaser buff Print the contents of the output buffer OK if the operation uccessful Out of
7. STARt Resetting see OUTPut SCAN RESEt Wavelength Set see SOURce WAVElength Starting any of the above three operations clears the OPC status bit When the laser reaches the target wavelength the OPC status bit is set to 1 The bit is also set to 1 if the movement is interrupted either with SCAN STOP which interrupts a SCAN or RESEt or OUTPut TRACk OFF which interrupts a Wavelength Set During a wavelength scan ROREP gt 0 and when the scan is completed AOE CS gt l OUTPUT COMMANDS Command Description Explanation Example W OUTPut SCAN RESEt Retum to start wavelength The wavelength is reset to the start wavelength at the retum slewrate Ifa scan is in progress it will be interrupted and the wavelength reset to the start wavelength Works the same whether laser is in Remote Mode or Local Mode The OPC command will return 0 until the start wavelength is reached The current wavelength is 672 nm the Start Wavelength is 670 0 nm and the Return Slew Rate is 100 percent OUTP SCAN RESET gt OK The laser wavelength is changed at the maximum rate until the wavelength 670 0 nm is reached 43 44 Command Description Explanation Example W OUTPut SCAN STARt Start restart a wavelength scan Begins scanning from the current wavelength to the stop wavelength at the forward slew rate Works the same whether the laser isin Remote Mode or Local Mode Th
8. This translates into a tunable laser with no mode hops That s the basic theory behind the cavity design In the next section we ll show how the theory is put into practice by describing the components of the New Focus 6200 series laser system Figure 2 Drawing of important angles and optimum pivot point 10 W References 1 2 3 4 5 6 M G Littman and H J Metcalf Spectrally narrow pulsed dye laser with out beam expander Applied Optics vol 17 p 2224 2227 1978 M G Littman Single mode operation of grazing incidence pulsed dye laser Optics Letters vol 3 p 138 140 1978 K Liu andM G Littman Novel geometry for single mode scanning of tunable lasers Optics Letters vol 6 p 117 118 1981 M G Littman Single mode pulsed tunable dye laser Applied Optics vol 23 p 4465 4468 1984 K C Harvey and C J Myatt External cavity diode laser using a grazing incidence diffraction grating Optics Letters vol 16 p 910 912 1991 T Day E Luecke and M Brownell Continuously tunable diode lasers Lasers and Optronics p 15 17 June 1993 Il Description of Laser System W Controller The controller s job is to provide a stable low noise power source for the diode laser set the temperature in the laser head command wavelength scanning and provide readouts of all relevant laser parameters Conceptually the cir cuitry inside
9. W SENSe TEMPerature SETPoint DIODe Read diode temperature set point Retums the current temperature set point for the laser diode gain element in degrees Celsius This value is exactly the same as the set point that appears on the front panel ofthe laser The diode temperature is maintained by an analog control loop This command retums the measured set point of the control loop This value can be changed either from the front panel or with the SOURce TEMPerature command The diode temperature set point is 21 1 C SENS TEMP SETP D Ol DE gt 21 1 53 Command Description Explanation Example 54 W SENSe TEMPerature SETPoint CAVity Read cavity temperature set point Returns the current temperature set point for the laser cavity in degrees Celsius This is the only way this value can be read it cannot be read from the front panel The cavity temperature is actively controlled at about 30 C This command retums the set point for the control loop inside the controller This quantity is set at the factory and cannot be changed by the user SENS TEMP SETP CAV gt 30 0 Command Description Explanation Example W SENSe VOLTage LEVel PIEZo Read piezoelectric voltage setting lt value 0 100 gt Retums the current piezo voltage setting in percentage of maximum from 0 to 100 percent This value is the same as that which appears on th
10. active again 75 W Example WINP ON gt OK Track LED flashes Wavelength changes to voltage specified by value at Wavelength Input jack on back panel of controller Encoder and Scan button are disabled WINP OFF gt OK Track LED stops flashing Wavelength movement stops at current value Encoder can now change wavelength Scan button is active 76 Command Description Explanation W SYSTem MCONtrol lt wsp gt lt INT EXT gt Puts controller into Local Mode internal or Remote Mode external Forces the laser to use intemal DACs or front panel potentiometers for control of piezo voltage diode temperature set point and diode current EXT If the laser is already in Local Mode Command has no effect If the laser is not in Local Mode Control of diode temperature set point diode current and piezo voltage is retumed to the front panel potentiometers NOTE The pots are absolute not relative so if they have changed the values will reflect that change INT If the laser is already in Remote Mode Command has no effect If the laser is not in Remote Mode Diode temperature set point diode current and piezo voltage are sensed and used as targets for the DACs Front panel displays will change as sensed and target values can differ by up to 3 due to component variations such as resistor tolerances Note that in Remote Mode the front panel potentiomete
11. is given to the DACs The piezo control DAC is driven to a voltage which produces the requested percentage to within 3 W The diode current control DAC and the temperature control DAC are driven to voltages which produce values within 3 of the value they had under front panel potentiometer control The laser is nowin Remote Mode Explanation Query Form If the laser wasin Remote Mode Remote LED is already on The current piezo voltage and diode temperature are unaffected Retumsthe the last piezo control percentage sourced If the laser wasin Local Mode Remote LED comes on Control of the laser is given to the DACs The Piezo control DAC is driven to a voltage which produces a percentage within 3 of the value it had under front panel control The current control DAC and the temperature control DAC are driven to voltages which produce values within 3 of the value they had under front panel potentiometer control The laser isnowin Remote Mode Retumsthe target piezo control percentage which is the front panel percentage at the moment the query occurred Example Front panel shows the following Remote LED off Local Mode Piezo voltage reads 30 1 Diode temperature set point reads 20 0 Diode current reads 59 2 65 66 W VOLT 66 8 gt OK Front panel now shows Remote LED on Remote Mode Piezo Voltage reads 64 9 Diode temp set point reads 19 7 Diode curr
12. nflaser WAVELENGTH START STR wavelength INPUT What stop wavelength would you like nm wavelength CALL IBWRT nflasers WAVELENGTH STOP STR wavelength Set forward and return scan speeds to their maximum values CALL IBWRT nflaser WAVELENGTH SLEW FORW 100 CALL IBWRT nflaser WAVELENGTH SLEW RET 100 Get ready to scan CALL IBWRT nflaser OUTPUT SCAN RESET PRINT Tuning to the start wavelength Wait until laser gets to start wavelength Here we use th OPC operation complete query to see if OUTPUT SCAN RESET has finished ready 0 WHILE ready 0 32 W CALL IBWRT nflaser OPC CALL IBRD nflaser buff ready VAL buff WEND Start scan PRINT Push any key to begin the scan WHILE INKEY W WEND CALL IBWRT nflaser OUTPUT SCAN START END 33 34 VI Command Summary W With GPIB and for programs written in QuickBAsic all commands are issued using the IBWRT function call in a program To read the controller s response to a command use the IBRD function call For RS 232 operation use to get the attention of the controller before starting command entry and end each command with a carriage retum lt a gt The controller s response is automatically sent The portions of commands in square brackets are optiona
13. the maximum voltage is exceeded the diode laser will tune to its maximum wavelength and stop Then the wavelength readout will flash indicating you have exceeded the maximum input voltage The laser will then be kicked out of Wavelength Input Mode into Track Mode The same thing happens if you input a voltage less than the voltage corresponding to the minimum wavelength To stop the flashing either hit the local button or use the wavelength control knob to shift the wavelength a few angstroms off the edge To exit Wavelength Input Mode push the two paddle switches down at the same time The LED will stop flashing the wavelength will remain where itis and the controller will retum to Track Mode Note that the wavelength control W knob is disabled while the laser is in Wavelength Input Mode Also if you exit Track Mode and then re enter the laser will still be in Wavelength Input Mode Finally note that the wavelength that results from applying a voltage to the Wavelength Input jack is not a linear function of the input voltage The input impedance of this control is 5 kQ Detector Input The Detector Input is a 10 bit analog to digital converter input to the micro processor Analog signals that you connect here can be read out by your com puter when you use remote control Thisis a general purpose input that allows you to collect data from a photodetector during a wavelength scan or for example to create your own constant power
14. wavelength starts changing at the maximum rate until it reaches 670 25 nm The wavelength display will probably flicker between 670 2 and 670 3 as thisis the round off point Note that you can use OPC to determine when the wavelength change has been completed W Command Control Form SOURce WAVElength SLEWrate FORWard lt wsp gt lt value gt Query Form SOURce WAVELength SLEWrate FORWard Description Write and read the forward slew rate for a wavelength scan Explanation Control Form This command does not affect and is not affected by whether the laser is in local mode or remote mode 1 lt VALUE lt 100 The units are in percentage of the maximum rate Ifthe value is out of range Returns Out of Range No other action is taken Ifthe value is in range Returns OK Forward wavelength slew rate is set to the desired value The 1 to 100 value is translated into a voltage on the picomotor control board The actual speed is not linear with this voltage As you increase the slewrate from 1 to 100 the actual wavelength rate of change does not always increase The slewrate only affects scanning The slewrate during a wavelength change from a SOURCE WAVELENGTH command is always 100 Explanation Query Form Returns the current forward slew rate 69 70 Example w The laser is scanning from the start to the stop wavelength and the following commands are executed WAVE SLEW
15. AVE 672 4 nm com mand The Track LED is on OUTP TRACK OFF gt OK The laser is still at 672 4 nm but is now in Ready Mode the quiet mode of operation The Track LED is off Command Description Explanation Example W OUTPut STATe lt wsp gt lt OFF ON 0 1 gt OUTPut STATe Tums the laser on and off reads whether the laser is on or off ONor1 I fthelaserisON no action is taken If the laser is OFF the Laser Power switch LED blinks and after 5 seconds the laser is turned on and the LED is steadily on OFF or 0 IfthelaserisON orin the intermediate blinking state the laser turns off and the Laser Power switch LED tums off If the laser is already OFF no action is taken Returns 1 if the laser is on and 0 if itis off Works the same whether the laser is in Remote Mode or Local Mode The front panel Laser Power switch is off OUTP gt 0 OUTP ON gt OK The Laser Power switch LED begins to blink OUTP gt 0 After 5 seconds have elapsed the LED is solidly on and the laser is on OUTE gt 1 47 SENSE COMMANDS Command Description Explanation Example 48 W SENSe CURRent LEVel DIODe Read diode laser current level Retums the magnitude of the laser diode current in milliamps The value returned is the same as that seen on the front panel of the controller at the time the command is executed Front panel current reading is
16. Diode laser power at the wavelengths shown in the table above could be accessible in the interior of the laser head The laser light emitted from this unit may be harmful to the human eye Avoid looking at the laser beam directly The safety labels shown on the fol lowing page are attached to this product W Safety Warning Labels ID Certification Label Aperture Label Il Introduction W The New Focus 6200 series External Cavity Tunable Diode Laser is a stable narrow linewidth source of tunable light The 6200 series laser can be operat ed manually from the front panel of the controller or remotely using comput er control In this section we ll describe the key features of the 6200 series and explain some of the theory of external cavity diode laser design In Section III page 11 we give a thorough description of each part of the 6200 system Section IV page 15 covers manual operation while Section V page 26 goes over computer control of the laser system Section VI page 34 has detailed expla nations of the computer control commands and error codes are listed in Section VII page 78 The AC operating voltages of the controller are detailed in Section VIII page 79 and service and support are described in Section IX page 81 Finally a table of specifications is given in Section X page 82 Features The 6200 series laser incorporates a simple stable mechanical design with a minimum number of optical co
17. FORW 1 gt OK The wavelength now changes very slowly WAVE SLEW FORW 100 gt OK The wavelength now changes at its maximum rate WAVE SLEW FORW gt 100 0 W Command Control Form SOURce WAVELength SLEWrate RETurn lt wsp gt lt value gt Query Form SOURce WAVElength SLEWrate RETurn Description Writes and reads the retum slew rate for wavelength scans Explanation Control Form 1 lt VALUE lt 100 The units arein percentage of maximum rate This command does not affect and is not affected by whether the laser is in local mode or remote mode Ifthe value is out of range Returns Out of Range No other action is taken If the value is in range Returns OK The return wavelength slew rate is set to the desired value The 1 to 100 value is translated into a voltage on the Picomotor control board The actual speed is not linear with this voltage As you increase the slew rate from 1 to 100 the actual wavelength rate of change does not always increase The slew rate only affects scanning The slew rate during a wavelength change from a SOURCE WAVELENGTH command is always 100 Explanation Query Form Returns the current return slew rate 71 72 Example v The laser is resetting from the stop to the start wavelength and the following commands are executed WAVE SLEW RET 1 gt OK The wavelength now changes slowly WAVE SLEW RET 100 gt
18. In Ready Mode the laser runs open loop without W active wavelength control Because of the nature of the wavelength control scheme however note that the wavelength of the laser is significantly more stable in Ready Mode than it is in Track Mode With the laser in Track Mode you can set the wavelength by rotating the Wavelength Adjust knob Note that the display shows 0 01 nanometer resolu tion for setting wavelength but only 0 1 nanometer resolution once the oper ating wavelength is established This is because the precision with which you can set the wavelength is greater than the accuracy of the wavelength read out When you select a new wavelength with the Wavelength Adjust knob the Picomotor moves the end mirror until the new wavelength is reached Because of the slow speed of the Picomotor the Picomotor may continue to scan for a period after you have finished scanning the laser to reach the desired wavelength setting the wavelength on the display From inside the laser head you can hear the Picomotor s characteristic whining or clicking sound as it moves the mirror Setting the Temperature To set the temperature hold the multipurpose scanning and temperature paddle switch to the left of the Temperature Adjust knob up toward Diode While you are still holding the switch up tum the Temperature Adjust knob until the Temperature readout shows the number you want to set After you let the multipurpose switch go the Tempe
19. Model 6200 User s Manual The External Cavity Tunable Diode Laser Patent No 5 319 668 CAUTION Use of controls or adjustments or performance of procedures other than those specified herein may result in hazardous radiation exposure V Contents 620221 Rev D 2 I II III IV MI VIII IX User Safety Introduction Description of Laser System Manual Operation Computer Control Command Summary Error Codes AC OperatingVoltages Service and Support Specifications 15 26 34 78 79 81 82 W User Safety Laser Safety Warnings W Your safe and effective use of this product is of utmost importance to us at New Focus Please read the Laser Safety Warnings before attempting to operate the laser Note To completely shut off power to the unit unplug it from the wall Table 1 Model Max Power Wavelength Range 6210 25mW 620 645 nm 6202 25 mW 645 700 nm 6224 50 mW 700 800 nm 6226 75 mW 800 900 nm 6238 75 mW 900nm 1 2um 6248 20 mW 1 2 1 4 um 6262 20 mW 1 4 1 6 um Table of maximum internal powers and possible wavelength ranges by model number Note The user will NEVER need to open the laser head Contact New Focus if for some reason you want to open the laser head Unauthorized open ing of the laser head will void the warranty and may resultin mis alignment of the laser cavity and or irreparable damage to the internal com ponents
20. OK The wavelength now changes at its maximum rate WAVE SLEW RET gt 100 0 Command Control Form Query Form Description Explanation Control Form Explanation Query Form Example W SOURce WAVElength STARt lt wsp gt lt value gt NM ANG SOURce WAVElength STARt Read and write the start wavelength for a scan This command does not affect and is not affected by whether the laser is in Local Mode or Remote Mode MIN lt VALUE lt MAX MINand MAX arelaser dependent See SOURCE WAVELENGTH2MIN MAX for details The default units are nanometers NM ANG indicates angstroms If the value is out of range Returns Out of Range No other action is taken If the value is in range Retums OK Start wavelength is given a new value ow Retums the current start wavelength The start wavelength is 772 nm and the following commands are executed WAVE START 770 gt OK The start wavelength is now 770 nm WAVE START gt 770 0 73 Command Control Form Query Form Description Explanation Control Form Explanation Query Form Example 74 W SOURce WAVElength STOP lt wsp gt lt value gt NM ANG SOURce WAVElength STOP Writes and reads the stop wavelength set point for wavelength scans This command does not affect and is not affected by whether the laser is in Local Mode or Remote Mode MIN lt VALUE lt MAX Th
21. Range if wavelength is not valid etc was s PRINT PRINT buff Return to local control CALL IBONL nflaser 0 END 30 Example 2 W Thisis the same asthe last program except that this time we use RS 232 communications instead of GPIB sk user for a wavel Ask f Length in nanometers wavelength is a single precision floating point number 775 1 for example INPUT What wavelength would you like nm wavelength RS 232 commands should be preceded by e MESSAGES WAVE STR wavelength Open the serial communications RS 232 port with baud rate 9600 8 data bits no parity and 1 stop bit OPEN COM2 9600 N 8 1 ASC CDO0 CS0 DS0 0P500 RS TB512 RB512 FOR RANDOM AS 1 Send the message to the controller PRINT 1 MESSAG ES Read and print the response from the controller LINE INPUT 1 R ESPONS PRINT RESPONSE Close the port CLOSE 1 END ES 31 W Example 3 This program sets up and executes a wavelength scan using GPIB Be sure to look at Example 1 before reading this program INCLUDE gbdecl bas CLS buff SPACE 32 Find the laser controller at GPIB address 1 CALL IBDEV 0 1 0 T10s 1 0 nflaser CALL IBCLR nflaser Set up start and stop wavelengths INPUT What start wavelength would you like nm wavelength CALL IBWRT
22. T PEAK TO PEAK INPUT AVOID STATIC DISCHARGE Since this is a direct connection to the diode laser there is no current limiter that prevents too much current from passing through the diode Thus there isa danger of destroying the diode laser if the maximum current is exceeded Be sure that the current modulation applied to the diode laser will not result in driving the diode laser above its maximum current See included Data Sheet The high speed input has a protective shorting cap which should remain in place in normal operation When removing the shorting cap to connect an high frequency driver be sure to wear a ground strap to prevent static dis charge Please contact New Focus if you have any questions on how to use the high speed modulation input Wavelength Output The Wavelength Output BNC jack provides a signal from 0 to 10 Vthat corre sponds linearly to the laser output wavelength This connection has 3 kQ output impedance Zero volts are output at the minimum operating wave length for the laser head connected to the controller The voltage increases with wavelength according to the equation V f AA where AA isin nanometers and the parameter f depends on the particular laser center wavelength Typically fis between 0 2 and 1 W nm See the Acceptance Test Data Sheet for the particular Wavelength Output characteris tics of your laser Wavelength Input The Wavelength Input jack is for coarse analog control of the wavel
23. de the allowed range or Unknown Command if the command was not recognized Ifthe command isa Source Query or a Sense Command the controller will retum a value or Unknown Command if the command was not recognized For example you send WAVELENGTH lt cr gt and you get back 671 8 RS 232 communications may be performed at 300 1200 2400 4800 9600 or 19200 baud The data format is 8 bits no parity with 1 stop bit The laser must be in Ready Mode to change the controller s baud rate Press the Local button and hold the Scan Speed paddle switch down at the same time The wavelength control knob then steps you through the baud rates Programming examples Next we present three elementary programs written in QuickBasic These example programs demonstrate the basics of talking to your controller through GPIB or RS 232 The section that follows these programming examples details the entire com mand set and describes the use and syntax of all the commands W Example 1 This simple QuickBasic program asks the user for a wavelength and then tells the laser to tune to that wavelength If you are using a National Instruments GPIB card in your computer be sure to read the file GPIBPC QBASIC README QB for instructions on using the QuickBasic interactive environment with GPIB Other manufacturer s cards will have similar instructions The next line must be included for QuickBasic to work with a National Instruments
24. e MIN and MAX values are laser dependent See SOURCE WAVELENGTH2MIN MAX for details The default units are nanometers NM ANG indicates angstroms Ifthe value is out of range Returns Out of Range No other action is taken Ifthe value is in range Retums OK Stop wavelength is set to the new value Retums the current stop wavelength The stop wavelength is 776 nm and the following commands are executed WAVE STOP 774 gt OK The stop wavelength is now 774 nm WAVE STOP gt 774 0 SYSTEM COMMANDS Command Description Explanation W WINPut lt wsp gt lt 0 1 OFF ON gt Enables and disables Wavelength Input Mode This command works the same in both Local Mode and Remote Mode ONor 1 All wavelength activity such as scanning or even moving to a newly sourced wavelength is halted The laser will immediately begin moving to the wavelength correspond ing to the voltage at the Wavelength Input jack The controller does not have to be in Track Mode to execute this com mand Track Mode is entered on execution of this command The Track LED will flash on and off signifying that the Wavelength Input is active Encoder and Scan button are disabled OFF or 0 The laser remains in Track Mode with the encoder active Wavelength motion stops Track LED stops flashing and remains on signifying Track Mode Encoder can now change wavelength The Scan button is
25. e OPC command will return 0 until the stop wavelength is reached The current wavelength is 670 0 nm the Stop Wavelength is 672 0 nm and the Forward Slew Rate is set at 50 percent OUTP SCAN START gt OK The laser wavelength is tuned at about half the maximum rate until 672 0 nm isreached Command Description Explanation Example W OUTPut SCAN STOP Stop pause a wavelength scan Stops a scan or reset if one is going on leaving the laser in Ready Mode Works the same whether the laser isin Remote Mode or Local Mode The OPC flag is set to 1 showing that the SCAN or RESET is stopped The laser is performing a scan and then the following commands are issued to the controller OPC gt 0 OUTP SCAN STOP gt OK OPC gt 1 The scan is stopped the controller isin Ready Mode and the wavelength is set to the wavelength the laser was at when the OUTP SCAN STOP command was issued 45 46 Command Description Explanation Example W OUTPut TRACk lt wsp gt OFF Exit Track Mode to Ready Mode Takes the laser out of Track Mode and placesit in Ready Mode the quiet mode of operation Note that issuing a SOURce WAVElength command for instance will place the laser in Track Mode and OUTPut TRACk OFF is the way to get back into Ready Mode Works the same whether the laser is under front panel or DAC control The laser wavelength has been set to 672 4 nm with a W
26. e front panel of the laser Note that as the piezo voltage increases the lasing frequen cy increases and the wavelength decreases The piezo voltage is 66 8 percent of its maximum SENS VOLT PIEZ gt 66 8 55 56 Command Description Explanation Example W SENSe VOLTage LEVel AUXiliary Read voltage at the Detector Input lt value 0 5 volts gt Retums the voltage at the auxiliary Detector Input on back panel of the laser controller The value retumed is from 0 to 5 volts This is the only way this value can De read it cannot be read on the front panel The resolution for the Detector Input is 10 bits so the step size is 5 1024 4 88 mV The Detector Input sees 1 22 volts SENS VOLT AUX gt 1 22 Command Description Explanation Example W SENSe WAVElength Read laser wavelength lt valuenm gt Retums the current wavelength of the laser in nanometers This value will match the front panel display exactly Each laser is calibrated with respect to wavelength at the factory and a calibration table loaded into the laser head The wavelength set by a Source Command will match the sensed wavelength to the number of decimal points retumed The number of decimal points depends on the accuracy of the angle measurement technique used to mea sure the wavelength Currently the accuracy of this measurement is 0 1 nm The wavelength is 679 63 nm SENS WAVE gt 679 6 57
27. e laser isin Remote Mode For this reason if any of those three parameters are queried while the laser isin Local Mode the laser is placed in Remote Mode with the current temperature set point and piezo voltage taking on the last front panel values they had before the switch Sense Commands return the value of various laser operating conditions Note that there is an important difference between Sense Commands and Source Queries Sense Commands read actual voltages currents temperatures or wavelengths the value returned is the same as that seen on the controller front panel at the time the command is executed In contrast Source Queries read set points values that are theoretical goals These values may not nec essarily match the values displayed on the front panel For instance the queried diode current and piezo voltages can differ from the actual values by up to 3 due to component variations such as resistor tolerances However in the case of wavelength queries the wavelength set by a Source Command will match the wavelength retumed by a Source Query because each laser is facto ry calibrated and has its specific wavelength calibration table loaded into the laser head The next four pages have an index of all the possible computer control com mands Then the pages that follow the index of commands give detailed information about each command including a description of the command and examples of how the command is used Index
28. e temperature of the laser diode gain element in degrees Celsius This value is exactly the same as that which appears on the front panel of the laser The diode temperature is actively controlled Ifthe room temperature ever gets so high that the coolers have insufficient capacity to reduce the tempera ture the control loop can become unstable and destroy the cooling elements To prevent damage the laser is automatically shut down if the laser diode gain element temperature exceeds 35 C The diode temperature is 21 1 C SENS TEMP LEV DIODE gt 21 1 51 52 Command Description Explanation Example W SENSe TEMPerature LEVel CAVity Read cavity temperature Retums the temperature of the laser cavity in degrees Celsius This value is exactly the same as that which appears on the front panel of the laser The laser cavity temperature is actively maintained by the controller at about 30 C There is no command to set or change the cavity temperature set point Ifthe room temperature gets high enough that the coolers have insufficient capacity to reduce the temperature the control loop can become unstable and destroy the cooling elements To prevent damage the laser is automatically shut down if the laser diode gain element temperature exceeds 35 C The laser cavity temperature is 30 0 C SENS TEMP LEV CAV gt 30 0 Command Description Explanation Example
29. electric Peltier elements in the laser head Precise temperature con trol is achieved through the use of a two stage system One thermoelectric ele ment maintains the overall temperature of the laser cavity while another is specifically dedicated to the diode temperature within the cavity In this way the laser temperature is stabilized to within plus or minus one millikelvin while the temperature of the surrounding environment stays constant to with in plus or minus 10 millikelvin The PZT driver board supplies 0 120 Volts to a piezoelectric fine tuning ele ment in the laser head Using the PZT system you can tune the wavelength smoothly with sub angstrom precision The Picomotor board controls the Picomotor which provides coarse wave length control and scanning A Picomotor is a patented design that uses a piezo to tum a screw In this case the screw controls the tilt of the tuning mir ror in the laser head Picomotor driven screws are available from New Focus for a variety of other applications as well The microprocessor board tells all the other boards what to do runs the digi tal displays and provides RS 232 and GPIB interfacing capability It also communicates with the circuit board in the laser head to determine what kind of laser head it is and to upload the wavelength calibration table Finally the mother hoard is the interface backplane for all the boards and also drives the LED displays W Laser head The laser
30. ength For example you could use it for your own analog wavelength scanning control The DC signal that you apply to the Wavelength Input is injected directly into 23 24 W the wavelength control loop You can scan it as fast as the fastest internally controlled scan If your analog control signal is not too noisy you should be able to control the wavelength in angstrom or even sub angstrom incre ments Note however that if you don t have a quiet analog control voltage this mode of operation has less wavelength stability than Track Mode Ifyou want to use the Wavelength Input jack you must first place the laserin Wavelength Input Mode To do this you must first be in the Track Mode Then push both front panel paddle switches scan speed and wavelength tempera ture multifunction up at the same time The wavelength display will show all ones 111111 and the Track light will begin to flash on and off The laser will immediately begin changing to the wavelength which corresponds to the voltage at the input Note that an unconnected wavelength input corresponds to zero volts and a mid range wavelength The Wavelength Input jack accepts DC signals between 15 and 15 V However the voltages that correspond to the maximum and minimum wavelength vary from laser to laser That is the voltage corresponding to the maximum wavelength is less than 15 V and the voltage corresponding to the minimum wavelength is greater than 15 V If for example
31. ength from the short wavelength side Coarse wavelength scanning is performed with the Picomotor inside the laser head that controls the angle of the end mirror Please note that the Picomotor lifetime is finite APicomotor has a total integrated lifetime of approximately 200 hours if operated at its maximum speed This means that a Picomotor can run at its maximum speed for a total of 200 hours If operated at a lower speed the lifetime is proportionately longer Therefore to prolong the life of the Picomotor inside the laser head it s a good idea to avoid unnecessary wavelength scans Setting the start and stop wavelengths Press the multipurpose scanning and temperature paddle switch up toward Start and hold it there The Wavelength readout changes when you do this to show you the starting wavelength for scanning You can now change the start of scan wavelength by tuming the Wavelength Adjust knob Note keep holding the multipurpose switch up 19 20 W Setting the end of scan wavelength is just as easy as setting the starting wave length This time you hold the multipurpose switch down toward Stop while you use the Wavelength Adjust knob to change the stop wavelength The laser will scan in whichever direction you set it The stop wavelength can be larger or smaller than the start wavelength Setting the scan speed The next step is to set the scanning speed If you hold the Scan Speed switch up you will see a number bet
32. ent reads 58 1 SENSE VOLT PIEZO gt 64 9 retumstheactual percentage VOLT gt 66 8 retumsthetarget percentage Command Control Form Query Form Description Explanation Control Form W SOURce WAVElength lt wsp gt lt value MIN MAX gt NM ANG SOURce WAVElength lt wsp gt lt MIN MAX gt Write and read the laser wavelength Drives the laser to the wavelength specified by lt value MIN MAX gt MIN lt VALUE lt MAX MINand MAX are laser dependent and may be queried see below NM indicates nanometers this is the default ANG indicates angstroms MIN _ Drives the laser to its minimum wavelength MAX _ Drives the laser to its maximum wavelength This command does not affect and is not affected by whether the laser is in Local Mode or Remote Mode If the value is out of range Returns Out of Range No other action is taken If the value is within the allowed range Retums OK Wavelength is set to the desired wavelength 67 68 Explanation Query Form Example W Retums the latest target wavelength The actual wavelength may be changing due to a newly sourced value or because the laser isin the midst of a reset ora scan MIN Retumsthe Minimum wavelength achievable with the laser MAX Returns the Maximum wavelength achievable with the laser Front panel displays wavelength 679 6 nm WAVE 670 25 gt OK The following occurs The
33. he instrument will send it into Remote Mode For example you can use a computer to mon itor all laser operating parameters while manually changing the wavelength from the front panel GPIB GPIB stands for general purpose interface bus It is also known as the IEEE 488 standard GPIB is a standard protocol for personal computers to commu nicate with laboratory instruments and several manufacturers make printed circuit board cards that plug into your computer and allowit to speak on the GPIB You will have to leam from the manufacturer of your GPIB card how to configure it to talk to an instrument at a given address and how to issue commands to it from your favorite programming language In QuickBasic for example commands are sent to the laser controller through the GPIB instructions IBWRT and IBRD IBWRT sends an instruction to the W controller IBRD reads the controller s response to the command Examples of controller responses are OK or 772 3 Setting the GPIB address To set the laser controller s GPIB address the controller must be in Ready Mode Press and hold the Local button while holding up the Scan Speed paddle switch on the front panel Then tum the Wavelength Adjust knob until the number of the address you want appears in the Wavelength readout dis play You can set the address to be anything from 1 to 31 In the examples that follow we assume that you set your laser controller to address 1 Note also
34. he surface of the tuning mirror forming the resonant laser cavity This is the lasing wavelength because it s the only one that will survive for many cavi ty round trips It follows then that we can tune the laser by changing the angle of the tuning mirror There is one very important innovation that gives us true continuous tuning with a minimum of mode hops In order to stay in one mode as we tune the laser the number of waves in the cavity must be kept constant even though the wavelength of the light in the cavity is changing The number of waves in the cavity is maintained by having the tuning mirror rotate around a specific pivot point The pivot point creates a relationship between the cavity length and the laser wavelength The laser wavelength is set by the standard law for diffraction of light off a grating A A sn6 sn A is the spacing between grooves in the grating while O and refer to the incident and diffracted angles of the laser beam measured from a line normal to the surface of the grating The length D of the cavity can be broken into two parts and h See Figure 2 If we call the distance from the pivot point to the place where the beam strikes the grating L we can see from the figure that Lsn 0 and b Lsin04 Therefore the total cavity length is L sin 6 sin Dividing the total cavity length by the wavelength shows that the total number of waves in the cavity is I A which isa constant
35. head embodies a simple ultra stable design which is shown in Figure 4 Everything is mounted on a solid metal base and enclosed in a sealed package You will never need to open the laser head to operate the laser Unauthorized opening of the laser head will void the warranty Figure 4 Laser head mechanical schematic Hagh Speed Current Moduksicn Inpart ipt iii 7 In this design a diode laser is used as the gain medium One end of the diode laser has a high reflectivity coating which acts as an end mirror of the exter nal cavity The other end of the diode has an antireflection coating The diode laser is bonded to a temperature sensor and a thermoelectric cooling block which maintains the diode temperature constant to within 1 millikelvin The laser beam radiating from the diode is collimated by a lens before strik ing a high quality diffraction grating The diffraction grating is precisely aligned at New Focus and its position is fixed with respect to the diode From the diffraction grating a fraction of the beam is directed to the tuning mirror The position of this mirror determines the operating wavelength of the laser 13 14 fw The tuning mirror is mounted on a stiff arm An angle sensor near the pivot point of the arm provides data for wavelength readout The other end of the arm is moved by a Picomotor screw and a piezoelectric transducer PZT The Picomotor makes coarse wavelength changes while the PZT is used f
36. ific amount on the order of 30 GHz to 30 GHz This fine frequency range varies from laser to laser see the technical specifications of your particular laser for the actual tuning range The Frequency Modulation input will accept signals from DC to 2 kHz 3 dB rolloff point Increasing voltage at the Frequency Modulation input corresponds to a decrease in piezo voltage and an increase in laser frequency or a decrease in laser wavelength This decrease in piezo voltage is effectively subtracted from the front panel knob setting and the front panel display reads the result Current Modulation Input The Current Modulation input allows you to modulate the diode current as fast as 1 MHz This input accepts 10 to 10 volts into a DC coupled 5 kQ resistive load and provides 0 2 mA V modulation This input is summed with the front panel setting Note that the front panel current read out does not reflect the modulation input High Speed Current Modulation For high speed current modulation up to 100 MHz an SMA jack on the laser head is provided This input is AC coupled the low and high frequency roll off points are 50 kHz and about 100 MHz The current modulation provided by this input is approximately 20 mA V To prevent damage to the diode laser the voltage swing on this input must be less than 1 Vp p W WARNING THIS IS A DIRECT RF CONNECTION TO THE DIODE LASER AND IMPROPER USE COULD DESTROY THE DIODE LASER DO NOT EXCEED 1 VOL
37. ine Freq Tuning Range 70 GHz 0 09 nm 70 GHz 0 10 nm 75 GHz 0 15 nm 60 GHz 0 14 nm Fine Freq M odulation Bandwidth 2 kHz 2 kHz 2 kHz 2 kHz Wavelength Stability lt 0 01 nm day lt 0 01 nm day lt 0 01 nm day lt 0 01 nm day Coarse Tuning Resolution 0 01 nm 0 01 nm 0 01 nm 0 01 nm Tuning Repeatability 0 1 nm 0 1 nm 0 1 nm 0 1 nm Displayed Wavelength Accuracy 0 1 nm 0 1 nm 0 1 nm 0 1 nm Max Coarse Tuning Speed 6 nm min 6 nm min 7 nm min 7 nm min Repeatability 0 1 nm 0 1 nm 0 1 nm 0 1 nm Linew idth 50 ms lt 300 kHz lt 300 kHz lt 300 kHz lt 300 kHz Linewidth 5 s S MHz lt S MHz lt MHz SMHz Side M ode Suppression 40 dB 40 dB 40 dB 40 dB Model Typical Center Wavelengths 965 975 nm 1305 1320 nm 1530 1550 nm Minimum Tuning Range 25 nm 45 nm 60nm Minimum Power 10 mW 2mW 2mW Minimum Mid Band Power 15 mW 3 mW 3mW Fine Freq Tuning Range 50 GHz 0 16 nm 50 GHz 0 29 nm 30 GHz 0 24 nm Fine Freq Modulation Bandwidth 2 kHz 2 kHz 2 kHz Wavelength Stability lt 0 01 nm day lt 0 01 nm day lt 0 01 nm day Coarse Tuning Resolution 0 01 nm 0 01 nm 0 01 nm Tuning Repeatability 0 1 nm 0 1 nm 0 1 nm Displayed Wavelength Accuracy 0 1nm 0 1 nm 0 1 nm Max Coarse Tuning Speed 8 nm min 10 nm min 10 nm min Repeatability 0 01 nm 0 1 nm 0 1 nm Linew idth 50 ms lt 300 kHz lt 300 kHz lt 300 kHz Linewidth 5 s S MHz S MHz MHz Side Mode Suppression 40 dB 40 dB 40 dB
38. ing The Power readout shows how much optical power the laser is emitting When the current display is solidly on the laser operates in a single longitudi nal mode However above a certain current level the front panel current dis play will begin to flash indicating that the laser could be operating multi mode This operating regime allows you to access higher output powers at the expense of single mode operation If you require single mode operation keep the current below the level where the display begins to flash W At this point you have a basic knowledge of how to use the laser You know howto tum it on change its wavelength and temperature and adjust the power output Ifyou have a way to monitor the laser wavelength with sub angstrom preci sion you will be able to see the effect of the varying the Piezo Voltage control Try tuming it while the laser is in Ready Mode You should be able to see the wavelength change smoothly over as much asa few angstroms If you adjust the Piezo Voltage control when the laser is in Track Mode the Picomotor will counter the piezo motion and try to keep the laser wavelength constant Scanning Once you have had a chance to test out the basic operation of the laser you are ready for wavelength scanning The laser cavity is carefully adjusted to give the best tuning performance when tuned from short to long wavelength Therefore when scanning the laser it is best to approach the desired wavel
39. l and can be omitted without affecting the command Also the lower case parts of com mands may be omitted lt wsp gt means white space either a tab or a space lt value gt isa floating point number OFFION 0 1 means OFF or ON or 1 or 0 is legal Multiple commands on a line are not allowed For instance if the controller receives WAVE 670 22 IDN it will change the wavelength to 670 22 but the Identification Query will be ignored Numbers may contain at most 15 characters In most cases however this constraint will not be an issue The number 670 22 will be read correctly but the number 0000000000000670 22 will be read as 67 The examples given on the following pages show the text to be included in the command and the response from the controller With RS 232 serial com munications the response is sent immediately and the user may process or ignore the data With GPIB communications the response is loaded into the output buffer and the user may read it with a GPIB read or else ignore it For instance the example for IDN appears as follows W IDN gt NEW FOCUS 6202 H1 00 C1 01 The IDN is the command that is sent to the controller either over GPIB or RS 232 The arrow symbol gt indicates the response from the controller which in this example is NEW FOCUS 6202 HL 00 C1 01 Types of Commands There are six general types of commands Standard Commands Output Commands Sense Commands Source C
40. l remote mode at any time pushing the Local button will restore local mode with full front panel control Fine Frequency Control The Piezo Voltage knob and readout are used for fine sub angstrom wave length tuning Apiezoelectric transducer PZT is used to make adjustments in the tuning mirror angle that are too small to make by Picomotor control of the micrometer screw The readout isin percent of the maximum PZT volt age from 0 to 100 The next block contains the wavelength scanning and temperature controls The Wavelength Adjust knob is a multipurpose control What it does depends on which other buttons you press at the same time Similarly the Wavelength readout can display operating wavelength scan speed scan start and stop wavelengths GPIB address and serial baud rate The Temperature Adjust knob and Temperature readout control the desired operating temperature and display the actual temperature respectively Wavelength Track Mode and Ready Mode Push the Track button above the Wavelength Adjust knob to make the button light up If the button is already lit you can try tuming it off and on again When the Track light is on the laser isin the Track Mode and you can use the Wavelength Adjust knob to change the wavelength When the Track light is off the Wavelength Adjust knob is disabled and the laserisin the Ready Mode In Track Mode the laser wavelength is actively controlled using the Picomotor that tumsthe end mirror
41. mode with an extemal detec tor The Detector Input will accept signals from 0 to 5 volts and presents a 10 kQ load 25 26 V Computer Control W Anything you can adjust from the front panel you can also adjust by comput er control The 6200 Series system gives you an unprecedented level of exter nal control over a high precision narrow bandwidth laser source Computer control lets your computer talk to the laser controller to set or read a variety of operating parameters and perform certain actions The controller is always in one of two operating modes Local Mode or Remote Mode The operating modeis independent of computer control or manual control The wavelength can be set in either operating mode The piezo voltage the diode temperature and the diode current on the other hand are all either controlled by the external knobs Local Mode as dis cussed earlier or all by internal digital to analog converters DACs that can be set remotely Remote Mode When any one of these DACs is set by com puter control all three are then forced into Remote Mode The unspecified values default to their front panel settings at the moment of the switch to Remote Mode Pressing the Local button retums the laser to Local Mode Back panel inputs and outputs are still active in Remote Mode Note that the con troller will allow communication over the computer interface without switch ing to Remote Mode Only commands which alter the state of t
42. mponents Low noise analog circuits precise ly set critical operating parameters such as diode temperature and current Digital control facilitates remote operation and computer interfacing The 6200 is a modular system The same control unit will work with any 6200 series laser head The control units work in both manual and remotely programmed modes and are compatible with RS 232 and GPIB addressing We ve incorporated Picomotor technology in the laser head to bring you hands free wavelength scanning capability You set the start and stop wave lengths and scanning speed and the microprocessor controlled Picomotor takes care of the rest The unique cavity design assures continuous tuning with minimal mode hopping W Five LED digital readouts display important operating parameters including wavelength and diode temperature Inputs are available for low speed 1 MHz and high speed 100 MHz diode current modulation Theory of Design The New Focus 6200 series tunable lasers take advantage of the broad gain bandwidths available in semiconductor diode lasers Most tunable lasers use liquid organic dyes for gain These dyes are notoriously messy toxic and diffi cult to use The all solid state diode laser design by comparasion is compact clean and efficient In addition to being widely tunable the 6200 series lasers offer narrow linewidths This is accomplished by using a laser cavity design that began at the Massachusetts Institu
43. nel temperature set point at the moment the query occurred Example Front panel shows the following Remote LED off Local Mode Piezo voltage reads 30 1 Diode temperature set point reads 20 0 Diode current reads 59 2 62 W TEMP 22 1 gt OK Front panel now shows Remote LED on Remote Mode Piezo Voltage reads 29 6 Diode Temp set point reads 21 8 Diode Current reads 58 4 SENSE TEMP SETP DIODE gt 21 8 returns the actual temperature set point TEMP gt 22 1 returns the target set point The diode temperature is changed until it becomes 21 8 C 63 Command Control Form Query Form Description Explanation Control Form 64 W SOURce VOLTage LEVel PIEZo lt wsp gt lt value gt SOURce VOLTage LEVel PIEZo Write and read the voltage level of the piezoelectric transducer 0 lt value lt 100 units arein percentage of full scale This command forces the laser into Remote Mode Ifthe value is out of range Returns Out of Range No other action is taken If the value is in range Retums OK Piezo voltage is changed If the laser isin Remote Mode Remote LED is already on The piezo control DAC is driven to a voltage which produces the requested percentage to within 3 The diode current and the diode temperature are unaffected If the laser is in Local Mode Remote LED comes on Control of the laser
44. nput to the con troller Tum on the AC power with the key switch on the left hand side of the front panel The calibration table GPIB address baud rate laser head serial num bers and other pertinent operating information stored in an EEPROM in the laser head are uploaded to the controller The LED displays will show the model number head software revision number and controller software revi sion number After a few seconds the display will become active Figure 5 Front panel of laser controller ie COPY a Tat ide Liu o LIJ o jj o o The top half of the front panel contains all the indicators and readouts while the lower half has control knobs to adjust operating parameters The AC Power key switch is the on off for the whole unit including the laser head When you push the Laser Power button it flashes for a 5 second safety 15 16 W delay and then lights up to indicate that current is flowing through the diode laser in the laser head unit This allows you to set up all the desired operating parameters with the AC Power on but before you actually start generating light The Addressed and Remote indicator LEDs are status indicators Addressed lets you know if your computer has established contact with the laser via GPIB or RS 232 while Remote indicates that the laser is actually in remote mode with temperature piezo voltage and laser current set by the computer If you need to cance
45. of Commands Standard Commands Output Commands Sense Commands IDN Identification Query OPC W Operation Complete Query lt value gt OUTPut SCAN RESEt Stop and return to start wavelength OUTPut SCAN STARE OUTPut SCAN STOP Stop Pause scan Start Restart scan OUTPut TRACk lt wsp gt OFF Exit Track Mode to Ready Mode OUTPut STATe lt wsp gt lt OFF ON 0 1 gt OUTPut STATe Read laser on off lt value 0 Off 1 On gt 9 Tum laser on off DI ENSe CURRent LI EVel ODe Read current level lt value mA gt SENSe POWer LEVel FRONt Read front facet power lt valuemW gt 37 SENSEe POWer LEVel REAR Read rear facet power lt value mW gt EMPerature LEVel DI W ODe Read diode temperature lt value deg C gt EMPerature LEVel CAVity Read cavity temperature lt value deg C gt EMPerature SETPoint DIODe SENSe SENSe SENSE Source Controls SOU 38 SOUI Rce SOU VOLTage LI Rce Rce Read diode temperature set point lt value deg C gt EMPerature SETPoint CAVity Read cavity temperature set point lt value deg C gt VOLTage LEVel PIEZo Read piezoelectric voltage lt value 0 100
46. ontrols Source Queries and System Commands Standard Commands allow you to get information about the laser head and to query whether an operation has been completed Output Commands tell the laser to start some action such as starting or stopping a scan or reset System Commands set the operating mode of the controller Source Controls set laser operating parameters These parameters fall into two categories Those that use the internal digital to analog converters DACs and those that do not The piezo voltage the diode temperature and the laser diode current can be controlled either from the front panel with potentiome ters or from voltages generated by intemal DACs The other parameters wave length scan speeds and scan start and stop wavelengths are independent of whether the potentiometers or the DACs have control When the front panel potentiometers have control the laser is considered to be in Local Mode When the intemal DACs have control the laser is consid ered to be in Remote Mode Setting any one of the three DAC parameters forces the other two under DAC control as well and the controller will be placed into Remote Mode The encoder Track and Scan buttons are locked out when the laser is in Remote Mode 35 36 W Each Source Control has an accompanying Query Source Queries retum the value of various controller set points A Source Query of diode current diode temperature or piezo voltage is only meaningful if th
47. or micron scale movements which corresponds to sub angstrom wavelength tuning precision The laser cavity is carefully adjusted to give the best tuning performance when tuned from short to long wavelength Therefore when scanning the laser it is best to approach the desired wavelength from the short wave length side Asmall fraction of the output beam is directed to a power monitor The read ing from this monitor is displayed on the front panel of the controller On the outside of the head enclosure you will see an SMA connector for high speed current modulation The use of this feature is described in Back Panel and Laser Head Connections in the next section Finally there is a monitor strip that indicates how many hours the diode laser has operated A new laser head will typically show 100 150 hours due to fac tory burn in The red monitor bar will slowly make its way across the window It will reach the other side when 5000 hours have elapsed IV Manual Operation W Using the Front Panel Before you start make sure the controller is plugged into a wall socket and your laser head cable is plugged into the back of the controller The cable has two plugs on it which fit into the sockets marked Cable A and Cable B Make sure you have the head pointed in a safe direction and check that the AC power input connector is configured for the correct line voltage See Section VIII page 79 for information about the AC power i
48. r Head Connections There are several input and output connectors on the back panel of the con troller They allow you to operate your laser with external analog or digital signals There are two connectors labeled Cable Aand Cable B for the cables that go from the controller to the laser head Cable A carries analog signals to the laser head while Cable B carries digital information Figure 7 Back pane of laser controller ni An Interlock connector is provided for external safety systems The laser will not emit light unless the Interlock terminals are shorted Five BNC connectors are provided for extemal analog control GPIB IEEE 488 and RS 232 are available for computer interfacing For information on computer control please see the next section of the manual Computer Control Analog BNC inputs and outputs are available for Frequency Modulation Current Modulation Wavelength Input Wavelength Output and Detector Input In addition there is an SMA connector on the laser head for high speed current 21 22 W modulation In the rest of this section we ll describe how each of these inputs and outputs works in detail Frequency Modulation Input The Frequency Modulation input is for external analog control of the PZT voltage It is useful for making fine frequency adjustments and for FM spec troscopy Sweeping the Frequency Modulation input from 3 Vto 3 V corre sponds to changing the laser frequency by a laser spec
49. rature readout will show the actual temperature which should soon become the set temperature Normally you will leave the temperature at the recommended operating tem perature shown on the Acceptance Test Data Sheet There may be certain wavelengths near the limits of your laser s tuning range where the light out put power will drop significantly This can happen because of residual etalon effects caused by small reflections at the antireflection coated facet of the diode laser In this particular case you will want to change the diode temper ature a few degrees and the power will be restored See Figure 6 pg 18 17 18 W Figure 6 Changing temperature to avoid power dips Diode Tempar iure Press the multipurpose scanning and temperature paddle switch down to check the cavity temperature The cavity temperature is factory set and active ly regulated to about 30 C If either the diode temperature or the cavity tem perature rises as high as 35 C the instrument will shut down Ifthe laser head is exposed to a severe thermal environment you should check the tem peratures to be aware of impending shut down Setting Current Power On the far right hand side of the panel you ll see the Current Adjust knob and the Power and Current readouts The current is set with the Current Adjust knob Do not worry about setting the current too high the controller knows the limits of the diode laser regardless of which head you re driv
50. rrent sourced If the laser was in Local Mode Remote LED comes on Control of the laser is given to the DACs The current control DAC is driven to a voltage which produces a current within 3 of the value it had under front panel control The temperature control DAC and the piezo control DAC are driven to voltages which produce values within 3 of the value they had under front panel potentiometer control The laser is nowin Remote Mode Retums the target current which is the front panel current at the moment the query occurred 59 60 Example W Front panel shows the following Remote LED off Local Mode Piezo Voltage reads 30 1 Diode temp set point reads 20 0 Diode current reads 59 2 CURR 26 4 gt OK Front panel now shows Remote LED on Remote Mode Piezo voltage reads 29 6 Diode temperature set point reads 19 7 Diode current reads 26 1 SENSE CURR DIODE gt 26 1 retums the actual current CURR gt 26 4 retums the target current Command Control Form Query Form Description Explanation Control Form W SOURce TEMPerature IEVel DIODe lt wsp gt lt value gt SOURce TEMPerature IEVel DIODe Write and read the temperature set point of the diode 16 lt VALUE lt 26 Theunitsarein C This command forces the laser into Remote Mode Ifthe value is out of range Returns Out of Range No other ac
51. rs are ignored but they are still active Ifa potentiometer is changed to an extreme setting and the controller is then switched back to external control the corresponding parameter will then move to the extreme setting 77 VII Error Codes 78 W The laser controller will indicate an error code in the wavelength display ifit is unable to perform its proper functions Some of these errors can be cleared by switching the laser controller off and then back on Ifthe errors persist please contact New Focus for assistance Errors 1 through 7 could indicate a broken or stuck switch Check the appro priate switch and if the errors persist contact New Focus Error 1 Error 2 Error 3 Error 4 Error 5 Error 6 Error 7 Error 8 Error 9 Error 10 Laser Power switch depressed during power up Scan button depressed during power up Track button depressed during power up Multifunction switch depressed during power up Scan Speed switch depressed during power up Local button depressed during power up Multiple stuck buttons during power up No head is connected to the controller or compatibility plug for 6100 series lasers is missing Cavity temperature at or greater than 35 C Make sure the laser head is heat sinked Diode temperature at or greater than 35 C Make sure the laser head is heat sinked These errors indicate a hardware problem If these errors persist contact New Focus Error 11 Error 12 Error 13
52. t MIN MAX gt Read output wavelength set point lt value nm gt WAVElength SLEWrate FORWard Read forward slew rate set point lt value 0 100 gt WAVElength SLEWrate RETurn Read retum slew rate set point lt value 0 100 gt 39 40 W SOURce WAVElength STARt Read scan start wavelength set point lt value nm gt SOURce WAVElength STOP Read scan stop wavelength set point lt value nm gt System Commands SYSTem WINPut lt wsp gt lt 0 1 OFF ON gt Enables and disables Wavelength Input Mode SYSTem MCONtrol lt wsp gt lt INT EXT gt Mode control Remote Mode DACs with Encoder Track Scan disabled Local Mode Front panel pots with all enabled STANDARD COMMANDS Command Description Explanation Example W IDN Identification Query Retumsthe following string identifying the instrument NEW FOCUS Model H Head Revision CI Controller Revision Model indicates the type of laser 6224 6202 etc Head Revision and Controller Revision indicate versions of software They will not necessarily be the same IDN gt NEW FOCUS 6202 H1 00 C1 01 41 42 Command Description Explanation Example W OPC Operation Complete Query Returns 0 if a long term operation is ongoing Retums 1 if no long term operation is ongoing The laser has three long term operations Scanning see OUTPut SCAN
53. te of Technology see refs 1 6 The original inven tors had dye lasers in mind when they worked out their cavity we have adapt ed the design to diode laser gain media Our version of the laser cavity is shown in Figure 1 Ahigh reflection coating on one end of the diode laser forms one end of the cavity and a high reflecting tuning mirror forms the other Starting from the diode the beam in the cavity passes through a collimating lens and then strikes a diffraction grating at near grazing incidence The beam is diffracted toward the tuning mirror which reflects the light back on itself for the reverse path Part of the light W Figure 1 Photograph of the lasar head with cover removed End Mirror Diode Laser Collimating Lens Picomotor Angle Sensor from the diode is reflected not diffracted by the grating This portion forms the output beam The grating functions as a narrow spectral filter Its passband is only a few gigahertz wide The high wavelength selectivity results because many lines of the grating are illuminated by the grazing incidence beam and because the beam is diffracted by the grating twice in each round trip through the cavity The grating spectral filter is narrow enough to force the laser to operate in a single longitudinal mode W Different wavelengths diffract off the grating at different angles However only one wavelength leaves the grating in a direction that is exactly perpendicular to t
54. that the GPIB address is stored in the laser head If you switch heads you should check to make sure that the second head has the same GPIB address as the first RS 232 RS 232 is a widely available standard for communication via your computers serial port You might want to use RS 232 to save yourself the expense of a GPIB card The one drawback is you can only talk to one instrument at a time with serial communication You will need to know howto send com mands to your computer s RS 232 serial port Any terminal emulation pro gram will let you send and receive via the serial port interactively RS 232 ports can be configured for operation in DTE or DCE mode The laser controller is configured as a DCE port This means that the laser controller receives data on pin 2 and transmits data on pin 3 For RS 232 operations use to get attention before starting command entry and end the command with a carriage retum lt a gt is the attention signal which must be the first character of each command string RS 232 commands are identical to the GPIB commands RS 232 commands are sent asa continuous string For example WAVE 671 84 lt cr gt The controller does not echo the command If you send an action command such as change the current or tune the wavelength the controller will 27 28 W retum one of the following responses OK if the command was properly executed Out of Range if a source value is outsi
55. the controller is built in two layers analog and digital The ana log layer incorporates low noise design for temperature current and wave length fine tuning The digital layer includes all the readouts and circuits to set operating points and scan parameters This layer acts as an interface between you or your computer and the analog layer Figure 3 Block diagram of circuit boards User Irpiri Local Gavtred Pane LEDS Laser Feediadicn Crt The analog layer consists of four printed circuit hoards the current board the temperature board the piezoelectric transducer PZT driver board which controls wavelength fine tuning and the Picomotor control board for coarse wavelength tuning The digital layer includes the microprocessor board and the mother board There is another digital circuit board in the laser head that 11 12 W contains information specific to each laser head such as a wavelength cali bration table and the laser head serial numbers The current board is a low noise analog DC current supply which provides up to 150 mAof current of either positive or negative polarity to the diode laser The AC ripple in the output is less than 0 4 pA RMS If desired the cur rent supply can be modulated up to 1 MHz through a BNCjack on the rear panel of the controller For proper operation use only with a cable shorter than three meters The temperature board controls the laser temperature by supplying current to thermo
56. tion is taken If the value is in range Retums OK If the laser was in Remote Mode Remote LED is already on The diode temperature set point control DAC is driven to a voltage which produces the requested set point within 3 The piezo voltage and the diode current are unaffected If the laser was in Local Mode Remote LED comes on Control of the laser is given to the DACs The diode temperature set point control DAC is driven to a voltage which produces the requested set point within 3 The current control DAC and the piezo control DAC are driven to voltages 61 W which produce values within 3 of the value they had under front panel Explanation potentiometer control Query Form Thelaserisnowin Remote Mode Ifthe laser wasin Remote Mode Remote LED is already on The current piezo voltage and diode temperature are unaffected Returns the last diode temperature set point Sourced Ifthe laser wasin Local Mode Remote LED comeson Control of the laser is given to the DACs The diode temperature set point control DAC is driven to a voltage which produces a current within 3 of the value it had under front panel control The current control DAC and the piezo control DAC are driven to voltages which produce values within 3 of the value they had under front panel potentiometer control The laser is nowin Remote Mode Retumsthe target diode temperature set point which is the front pa
57. ure 8 AC line power connector 80 IX Service and Support L Isa registered trademark of New Focus Inc W Warranty New Focus Inc guarantees its lasers to be free of defects for one year from the date of shipment or for 3000 hours of operation whichever comes first This isin lieu of all other guarantees expressed or implied and does not cover incidental or consequential loss Service and Calibration Your 6200 series laser has been designed to provide years of trouble free oper ation Virtually no maintenance is required except for ensuring that the unit isnot damaged contaminated or used in an unsafe manner To ensure lt 0 1 nanometer accuracy in wavelength readout the system should be recal ibrated every 6 months Any questions regarding the operation or perfor mance of the laser will be gladly answered by New Focus engineers For ser vice repair or calibration please call for a retum authorization number before shipping the unit to New Focus You can reach us at NEW FOCUS Inc 2630 Walsh Avenue Santa Clara CA95051 0905 USA Phone 408 980 8088 Fax 408 980 8883 Email Contact NewFocus com 81 X Specifications Table 2 Model 6210 6202 6224 6226 Typical Center Wavelengths 632 637 nm 670 675 nm 775 785 nm 840 850 nm Minimum Tuning Range 10nm 12 nm 15 nm 20 nm Minimum Power 2 mW 2mW 7mW 10 mW Minimum Mid Band Power 4mW 5mW 10 mW 15 mW F
58. ween 1 and 100 on the Wavelength readout This number is the scanning speed from the start wavelength to the stop wave length The units are relative 100 means the fastest possible speed while 1 is the slowest Experiment to find the best number To set the scan speed tum the Wavelength Adjust knob while holding the Scan Speed switch up The retum scan stop to start speed can also be set while holding down the Scan Speed switch Performing a scan To start a scan push the Scan button If the laser was in Track Mode the Track LED will tum off If the laser is at the start wavelength it will begin scanning at the scan speed Otherwise it will go to the Start wavelength at the retum scan speed and wait Push the Scan button again and the laser will begin scanning When the laser arrives at the Stop wavelength it will stop and wait there If you push the Scan button again the laser will reset to the Start wavelength There is a Trigger jack SMB type connector an SMB to BNC adapter is sup plied with the laser under the Scan Start Stop switch Voltage at this input rising above 3 Vand returning to zero is equivalent to depressing and releas ing the Scan button Stopping a scan Ifyou push the Scan button in the middle of a scan or a reset it will stop leaving you in Ready Mode If you push the Track button in the middle of a W scan ora reset the scan will be halted and the controller will bein Track Mode Back Panel and Lase
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