Beam Alignment System “Compact”
Contents
1. INNOVATIVE TREATMENT SOLUTIONS Beam Alignment System Compact User Manual i ion stabilizatto position a eam ctive ser B startistopP La Range Manual Beam Alignment System Compact version 6 October 14 2014 page of 19 INNOVATIVE TREATMENT SOLUTIONS Contents Wee OTST CL allt E E A E E N E ETE 3 Pe EE TEE a EA E pas E EE cares naa E AAE E A EE 3 1 EE HNC AU OI E E A EE E A A E A AE teen steed N A aimareueeent 4 Pk Me oe Mae ME a E AEE em EER 6 waonan O Oee E E E N 7 ddl Drei en Se Mein iO annn E EE EEEE EE 7 e E a O E EA EE AEA T 7 4A SCL UE OE ophcal componi essiri academe n EANET AREARE EER TTE a 8 dde TA O ERE EER E E E 10 E e E E E E S E E E I E PEA A 10 4 O Direction coding detector WULIIIG siicsiccsscsaveesatatwnadeieceerrsiqicsdiomeltaues Robes EERE iE Goes 11 4 1 Optimization of laser beam position on detectors cesses narsecscnsarvrinndexnsaonceetonicarersiecedasetiedbentaieeeddees 11 5 Operation and safety features cecececeeececececceceeccceeeceeceeeceeceaeeeeeeaeeeeeeeeeeeeeeeeeeeeeeeeeeeas 12 Dede Power level and OS I EY cee cass nnicexssenesacieseeeeepaneaiaas akinesia enemas 12 5 2 Variable intensity gain COM seisesidareeesinancedeeinssxdandachneteddnreancetennie deurtenanndaenennerdernernouseenerekiernenias 13 eLO N T T E A ene en eee ene enna etree eeere ater eren er erraer nae 13 s NG ll E E E aes ceca aaaoentse anaes amoneeras 13 S Ono ler otan i cE OEE EE EE 13 i Te A aao E2. They are very sensitive and can work with the leakage behind the mirrors This has the advantage that no additional components are required in the beam path Alternatively it is possible to use the reflection of a glass plate or beam splitter in the beam path The latter can be necessary for lasers with larger beam sizes where the actuator would constrain the transmission In any case the centres of the 4 QDs are positioned in that way that they define the desired laser beam direction The first actuator should be placed close to the laser or the last source of interference The last detector should be placed close to the target Note Take care for a robust mechanical mounting of the optical components If possible the delivered components should be directly tightened to an optical table without further positioning equipment like height adjustment If there are oscillating components with resonance frequencies within the control bandwidth in the set up such resonances can provoke oscillations of the system at that frequency The following figures 9a e show a selection of possible arrangements These examples are demonstrated with the 4 axes system with two 4QDs However they can be applied in similar configurations for the 2 axes system with only one actuator and one detector e Figure 9a shows a typical 4 axes set up of the system where the laser beam hits the optical components in the following sequence steering mirror co
3. components for the 4 axes stabilisation Detector I stabilises the beam position on actuator 2 Detector 2 then defines the beam position at a separate point and hence the direction detector 2 application a detector 1 actuator 2 actuator 1 laser beam Figure 9c Set up as in 9a but a lens is used to discriminate the angle by means of detector 2 This can be of advantage in case of restricted space with small distances between the optical components Detector 2 must be placed in the focal plane of the lens detector 2 application actuator 1 actuator 2 laser beam Figure 9b Set up as in 9a with an additional beam splitter and a lens in front of detector 1 and an additional lens in front of detector 2 Often used for lasers with larger beam diameters detector 1 detector 2 application actuator 1 actuator 2 laser beam Figure 9d In this set up both detectors are placed behind the same mirror Here the beam position and the direction are stabilised in close distance to the application Again as in figure 9c detector 2 is used to discriminate the angle Manual Beam Alignment System Compact version 6 October 14 2014 page 9 of 19 INNOVATIVE TREATMENT SOLUTIONS detector 1 GH application 1 actuator 1 Stage 2 AE actuator 2 beam splitter application 2 detector 2 laser beam Figure 9e Set up of a 4 axes system used as two 2 axes sy
4. the requirements of the European EMC Directive 89 336 EWG Labels SN 100208DBA036 SN 100208BA036 Model XY4QD 1kHz MRE Model 1kHz CW Supply 12VDC 0 2A i MRC Systems GmbH C Supply 12VDC 1A Germany MRC Systems GmbH Hans Bunte Str 10 D 69123 Heidelberg Germany Figure 18 Labels on the controller electronics left and on the detectors right Manual Beam Alignment System Compact version 6 October 14 2014 page 18 of 19 INNOVATIVE TREATMENT SOLUTIONS 10 Check list for laser data For the final layout of the system and for an optimal support of your integration it can be helpful to know your laser and set up data You can send us your data according to the following compilation CUORE a Feeccegnceacat E wavel ngth frange cavacecinconvvnnsecdansancdorendenscesdesctinets average laser powe azwsnasavendacsssasehsanavsesusoserecarsnenees p lse d ration ahewanizantnscnnedantosensteneeneseesnuastenstien fill in cw in case of a cw laser fepetition Tate eaeecrennssaacnacgscaceusevedesesenesennesce not applicable in case of a cw laser beam diameter sedesvadenpsiecedacdedenionsaceunpsasteastecntes Deam prolle aane qualitative specs as Gaussian elliptical etc are sufficient 10 1 Set up data If possible please send us a drawing or a photo or your intended set up We can then give you recommendations for the integration of the stabilisation system
5. the system Irreparable damage to the steering mirrors can occur Then check the laser power on the detectors and adjust it as described in section 4 5 Make sure that the initial laser beam has not changed strongly and that it hits the 4 QDs Take care that the beam is not blocked by an aperture or an edge anywhere in the beam path This could be the case at the cut out of the Piezo actuator If the red Range LED is on the closed loop control does not work in the linear range any more Please refer to section 4 5 then 8 5 Laser position is not stable If the automated stabilisation of the laser beam does not work although the controller is active this might be due to a wrong direction coding of the 4 QD inputs see section 4 6 Please check the direction coding Another reason might be an unstable mechanical set up leading to oscillations of the system Usually this phenomenon is accompanied by an exceptional humming noise E g high positions of components especially of those carrying the Piezo elements can lead to mechanical instabilities In this case a better stabilisation can be achieved with a lower controller bandwidth Please activate the bandwidth limitation switch see section 5 6 9 Safety The system has left our factory in a faultless state Please store and operate the system in dry environments in order to maintain this state C lt The device was designed and manufactured according to DIN EN 61000 3 2 and satisfies
6. ATIVE TREATMENT SOLUTIONS 7 3 Detector housing 9 Figure 17 Standard detector housing 8 Troubleshooting 8 1 No signals on display Please check if the power line chord is connected to a conducting power plug and if the power switch at the controller unit is activated If everything is okay with the power line please contact the manufacturer or distributor 8 2 No signals on detector Please follow the instructions in section 4 5 and check if an aperture or edge is blocking the laser If the laser beam hits the sensitive area of the detector another reason can be that the chosen filters are too strong In that case the filters should be exchanged 8 3 The laser beam is not correctly positioned Please check the following issues i Are all LEMO plugs x and y of each steering mirror correctly connected to the controller electronics ii Is the laser power in the allowed range iii If the red Range LED is on a Are all cables connected as described in section 4 4 b Is the initial position of the laser beam in an acceptable position If the initial position has changed strongly the closed loop control does not work in the linear range any more Please refer then to section 4 6 c Is the direction coding correct Manual Beam Alignment System Compact version 6 October 14 2014 page 17 of 19 INNOVATIVE TREATMENT SOLUTIONS 8 4 The steering mirrors make exceptional noise Please immediately switch off
7. SH detector with position display horizontal orientation detector vertical orientation Manual Beam Alignment System Compact version 6 October 14 2014 page 3 of 19 INNOVATIVE TREATMENT SOLUTIONS The system electronics controller amplifiers power supplies 1s fully integrated into a single compact housing It is powered by a standard 12V wall power supply Laser Beam Stabilization Star Stop Active Position Actuator 2 Directions H Bandwidth Figure 6 Power input and output connectors Figure 7 Input connectors and switches on left side 3 Specification Optical parameters Wavelength Repetition rate Laser beam diameter Height of laser beam Mirror diameter Mirror thickness on right side 320 to 1100 nm UV and IR detectors are available on request any rate or cw For repetition rates lt 100 Hz we integrate an adaptation for low repetition rates For single pulses and operations with laser off times we offer an additional sample amp hold circuit see also note 1 lt 6 mm 1 e see also note 2 45 mm for PKS actuators 39 5 mm for PSH actuators Please ask for adapters if you need other heights 1 standard other beam diameters on request 1 4 or 1 8 recommended Manual Beam Alignment System Compact version 6 October 14 2014 page 4 of 19 INNOVATIVE TREATMENT SOLUTIONS wxhxd 166 x 106 x 56 mm Type 1 PKS K 700 31 Actuator type Piezo electric e
8. We have our focus on an easy arrangement of the optical components and on appropriate distances between actuators and detectors arm lengths since they determine the reachable angular resolution 10 2 Actuated mirrors Please let us know if we shall provide the mirrors Who will provide the mirrors O Customer O MRC on request on account The following mirror sizes are recommended e standard diameter 1 thickness 1 4 1 8 as an alternative e on request diameter 1 5 and 2 11 Contact MRC Systems GmbH Hans Bunte Strasse 10 D 69123 Heidelberg Germany Phone 06221 13803 00 Fax 06221 13803 01 Website www irc systems de E mail info mrc systems de Manual Beam Alignment System Compact version 6 October 14 2014 page 19 of 19
9. cially in case of unstable mechanical set ups or if a mutual interference of the control stages occurs it can be of advantage to choose the low bandwidth Therefore a bandwidth limitation switch is integrated in the controller module Bandwidth see figure 7 H high L low bandwidth The bandwidth can be chosen independently for both stages Note The system uses the intensity centre of the transversal laser beam profile It does not reduce fluctuations of the laser beam profile itself Manual Beam Alignment System Compact version 6 October 14 2014 page 13 of 19 INNOVATIVE TREATMENT SOLUTIONS 6 Optical components 6 1 Steering mirror PKS The mirror mount PKS has a tilting range of 0 5 mrad which is smaller then the range of the PSH mount In comparison it offers a wider free space behind the mirror The mount can be adjusted manually for coarse adjustment Figure 12 shows a photo of this mount Figure 12 Steering mirror mount PKS with 1 mirror The blue arrows point to the x and y labels 6 2 Steering mirror PSH The mirror mount PSH has a wider tilting range of 1 mrad It can also be adjusted manually for pre adjustment to the zero position The mirror mount is optimized for low torque by means of reinforced springs and a balancing weight The standard mount is used with 1 mirrors But it can be equipped with adapters for bigger mirror sizes Figure 13a Steering mirror mount PSH Figure 13b Steer
10. ctuations or position movements of optical components occur but a high precision and stability of the beam stable application direction 1s required The desired position of the laser beam 1s 7 defined by a 4 quadrant diode 4 QD or a vibration 3 mechanical PSD For that purpose a small portion of drift See aii laser power transmitted through a high reflective deflection mirror is sufficient Figure 1 Principle of laser beam stabilisation The closed loop controller continuously determines the deviation of the laser beam from the desired position and drives the fast actuators in that way that the steering mirrors stabilise the laser beam in the desired position The system is available in two different models The 2 axes system comprises one detector and one steering mirror and controls the laser beam in two axes Thus the laser beam is fixed in one position but the beam direction can change The 4 axes system combines two detectors and two steering mirrors in order to detect the laser beam at two distant positions Thereby both position and direction are fixed 2 System components The laser beam stabilisation utilizes optoelectronic components steering mirrors detectors as well as electronic modules We offer different types of actuators and detectors For more details please check the specification in section 3 and the photos in section 6 Figures 2 3 and 4 from left to right Steering mirror with Piezo drive version P
11. d the Active LED is off This is due to the low power switch off that was implemented for safety reasons see section 5 3 Manual Beam Alignment System Compact version 6 October 14 2014 page 7 of 19 INNOVATIVE TREATMENT SOLUTIONS Figures 6 and 7 show both sides of the controller box with all input and output connectors and the switches for the Directions and the Bandwidth selection The cables going to the actuators are connected on the left side The cables coming from the 4 quadrant diodes are connected on the right side The direction switches enable a coding of the x and y directions of each controller stage They are connected with 4QD 1 and 4QD 2 respectively The performance is further described in section 4 6 The function of the bandwidth limitation switch is explained in section 5 6 The Status signal output can be used as an interlock or to drive a shutter see section 5 5 Note The Piezo elements have large electrical capacity That is why the cables should not be disconnected as long as the Piezo elements are charged I e you should always switch off the power of the stabilisation system on the left side of the panel and then wait for a few seconds before you disconnect the actuator cables 4 3 Set up of optical components The optical components steering mirrors and detectors can be configured in variable arrangements for different applications The detectors can be placed behind high reflection mirrors
12. display The total power on each connected 4 QD measured as the sum power on all quadrants is displayed by means of a LED bar on the backside of the detector module Furthermore a LED cross on the detector module displays the current laser beam position If the laser beam hits the centre of the 4 QD only the green LED of the position display will shine In other cases also yellow and red LEDs will shine according to the examples in figure 1 1 a peal c 6 b oe Ta d Figure 11 Examples for laser beams hitting the 4 OD orange spots and the corresponding position display The left pictures are shown in a view from the rear side of the housing to the sensor area If only green and yellow LEDs are shining the sensor electronics is in the linear range where a direct correlation between measured signal and position exists If a red LED is shining too the correlation is no more possible due to the principle of 4 QDs 5 2 Variable intensity gain control For an easy adjustment of the signal intensity the stepless potentiometer on the side of the detector unit can be used This enables the optimization of the power level in case of intensity changes without an exchange of optical filters The gain can be changed by a factor of 6 between the lowest and the highest value Manual Beam Alignment System Compact version 6 October 14 2014 page 12 of 19 INNOVATIVE TREATMENT SOLUTIONS 5 3 Low power switch off If th
13. e total power falls below 10 of the saturation power and only one LED of the power level display is on the controller module automatically drives the mirrors into zero position This leads to the advantage that the closed loop control can start from the zero position even if the laser was switched off or blocked 5 4 Switch on activity delay The integrated switch on activity delay starts the controller module not before a short time has passed and the steering mirrors have reached the zero position The Active LED will not shine during this delay 5 5 Controller status signal If the system 1s completely switched off power off the Piezo actuators tilt the steering mirror into an extreme position This is about 0 5 mrad PKS mount or 1 0 mrad PSH mount from the zero position However the system is equipped with a TTL output that can be used to block or electronically switch off the laser in order to avoid damage by the misaligned beam The level is HIGH whenever the controller module is active and the steering mirrors are in the correct range or in zero position It is LOW if the module is active and one of the actuators is out of range If the controller module is not active the level is always HIGH 5 6 Bandwidth limitation switch The controller bandwidth directly influences the quality of the stabilisation The system can be operated with two different controller bandwidths The default setting is the high bandwidth However espe
14. eree e e a SE E E S 13 Opare On 61 e e E ES 14 E TE E E AEE 14 Poea RN E E A E E EE EET EEE OEE EEEN AEE 14 ON Pw Detectors d guadrani diodes jesseni EEEE EERS 15 TADEN OS a E E seincu sede pceacenausvasensulnasaaes 16 a Mie aa eL aLa a N EIA EN PE EE EEE I E I E N TA E E T 16 Fe ON OE P aea tet ice hp N E EAE EAN EE EAA E EEA EEEE 16 Teee I E A E TEE AAEE EAA 17 Be cl OUI SOO PIN ae ie 17 EM PR aM Rc R gave assis EAE E EE extaveeenigs 17 T2 Tops PUN on 0c 5111 eee ae ces eee AEE E EE ato et Soyer mene este Se trey TE 17 8 3 The laser beam is n t correctly BORO oisecessnccesacentndaasavicersintmesdatearaseenentearnstixenteetuenranieiasieest 17 s4 The steering mirrors make Gx Ce DLO TIO1S Sc cntoesaratoscedcatecesakidootecunihinedieasviabieduaiasbseabededeeaccenteess 18 na Laer otter onto RE EREN 18 Og SS e EE E E E E E E E E 18 10 Check MET Vas Ch CA e E E 19 RE E E EROE A EARE A A ainaeas oss duadclnporte aed IA EIA SN C A cement 19 i Ue a Ty a e EOE IEE T N E E E E T E N EE EREET 19 C OMNI AG tears oat se net eee ee sete ett ee eee ee tee a eee ee ete 19 Manual Beam Alignment System Compact version 6 October 14 2014 page 2 of 19 1 General The Compact laser beam stabilisation compensates for vibrations shocks thermal drift or other undesired fluctuations of the INNOVATIVE TREATMENT SOLUTIONS closed loop controller laser beam direction The system should be ee stabilization target applied whenever laser flu
15. ge 1 stage 2 is still deactivated Then proceed according to section 4 7 10 For the stabilised operation of 4 axes activate both stages 4 2 Introduction The system operation can be described best with reference to figures 5 to 7 The top panel in figure 5 shows the keyboard and the position signal outputs for two pairs of detectors and actuators stage 1 and stage 2 Each stage can be switched on and off independently by pressing the Start Stop button If the stage is started the small LED in the top right corner of the button is shining The Range display shows whether or not the steering mirrors are within the available capture range The Active LED 1s shining whenever the control stage is active This is the case whenever the Start Stop button has been pressed and the laser power on the detectors has the right level The Position outputs on the top panel can be used to read out the current position of the laser beam on each 4 quadrant diode x and y Notes 1 Whenever the Start Stop button is pressed and the Active LED is on the actuators start to move from the zero position and then respond to the controller input 2 If a Range LED 1s shining red this does not automatically mean that the beam is not stable But it indicates that no further tilt of the respective steering mirror is possible although it might be necessary 3 If the power on the detectors is too low the actuators are driven to the zero position an
16. he housing With a tilt of the detector housing it should be possible to release the filters Once you put in new filters please be careful so that you do not damage the detector Finally you can fix them with the plastic screws Figure 10 4 quadrant diode The arrow points to the potentiometer for intensity variation Please use a screwdriver 4 6 Direction coding detector outputs For any deviation of the laser beam position on a 4 QD the respective steering mirror is tilted in that way that it adjusts the laser beam back to the desired position Each control stage makes use of a steering mirror and a 4 QD as described in sections 4 2 and 4 3 The components that are working together are identically coloured in figures 9 The direction in which the steering mirror must be tilted depends on the arrangement of 4 QD and steering mirror It can be changed during the pre adjustment process described in section 4 7 in the following way There are four switches on the right side of the controller module see figure 7 These switches stand for the x and y directions of the control stages Stage 1 and Stage 2 To turn them into the correct position just switch on the respective stage If the laser beam is then deflected into an extreme x horizontal and or y vertical position instead of the centre of the 4 QD you have to toggle the belonging switch 4 7 Optimization of laser beam position on detectors 1 Pre adjustment Obtaining linear
17. ing mirror mount PSH with 1 mirror with adapter for 2 mirrors Manual Beam Alignment System Compact version 6 October 14 2014 page 14 of 19 INNOVATIVE TREATMENT SOLUTIONS Notes e The movable plate of the Piezo elements is sensitive to mechanical forces Please avoid the impact of strong forces or torsional moments on this plate The Piezo stack is directly attached to this plate e Ifyou intend to remove the 1 5 or 2 adapter you should be especially careful We can provide a specific instruction and a tool for this purpose 6 3 Detectors 4 quadrant diodes Figure 14a shows the front side with the detection area of the standard 4 quadrant diode The outer dimensions of the PSD housing are identical Figure 14b shows the same side for the UV detector which is available on request Figure 14a Standard detector 4 quadrant Figure 14b UV detector 4 quadrant diode diode with sensitive area of 10x10 mm with sensitive area of 3x3 mm Manual Beam Alignment System Compact version 6 October 14 2014 page 15 of 19 INNOVATIVE TREATMENT SOLUTIONS 7 Drawings 7 1 Mirror mount PKS Figure 15 Mirror mount PKS For a better overview a typical path of a laser beam is displayed 7 2 Mirror mount PSH Figure 16 Mirror mount PSH For a better overview a typical path of a laser beam is displayed Manual Beam Alignment System Compact version 6 October 14 2014 page 16 of 19 INNOV
18. lements Bandwidth lt 700 Hz measured with 1 mirrors thickness 0 125 Maximum tilt lt 1 mrad 0 5 mrad Type 2 PSH K 102 10 Actuator type Piezo electric elements Bandwidth lt 840 Hz measured with 1 mirrors thickness 0 125 Maximum tilt lt 2 mrad 1 mrad Detector type Si 4 quadrant diode for standard wavelengths see also note 3 Bandwidth lt 10 kHz Detection area 10 x 10 mm for standard wavelengths see also note 3 Mechanical dimensions 49 x 40 x 20 mm Optical filter 11 9 x 11 9 mm Control features Power level display LED bar with 10 elements on the backside of the detector unit Position display LED cross on the backside of the detector unit Variable intensity gain Continuous adjustable with potentiometer 1 6 Low power switch off Power level falls below 10 of saturation power Switch on activity delay 300 ms Connectors at controller unit Actuator LEMO OS series Detector input LEMO OB series Controller status signal Interlock LEMO 00 series x y position output LEMO 00 series Power supply 12 V DC pin and socket connector Connectors at deteetors x y intensity outputs MCX Power 12 V DC pin and socket connector Cable lengths Detector Controller 2 cables 4 m other lengths on request Actuator Controller 2 cables PKS 1 5 m directly mounted to Piezo element PSH 1 2 m directly mounted to Piezo element Actuator Controller Elongation 10 m one pair of cables f
19. ler box Incase of the 2 axes system you can either use the first or the second stage for stabilisation 4 5 Intensity adjustment To make sure that the detectors operate in the linear range the power level can be adjusted by tuning the potentiometer for intensity variation see figure 10 For that purpose switch on the system Power on and inactivate the closed loop control Stop button switched OFF green Active LED and LED on button off Then adjust the laser beam onto the detectors in that way that at least 3 but not more than 9 elements of the power level display are shining The amplification increases by counter clockwise rotation Manual Beam Alignment System Compact version 6 October 14 2014 page 10 of 19 INNOVATIVE TREATMENT SOLUTIONS If you do not find an appropriate adjustment you have to exchange the optical filters in front of the 4 QDs If the required filters are not available please contact the manufacturer or distributor Notes e Ina standard delivery we integrate two optical filters in front of the sensor area These are a filters with a high and a low density for coarse and fine adjustment respectively Usually the filter which is the first to be reached is the low density one e Please be aware that the sensor area is quite sensitive If you want to clean it you should do this carefully with a dry cloth If you want to exchange the filters you can detach the plastic screws which fix the filters in t
20. mbination of steering mirror and detector mirror with detector e Figure 9b shows a similar set up where additional lenses are placed in front of the detectors Further a beam splitter is integrated in the beam path This set up might be better for lasers with large beam diameters In figure 9c a lens is placed in front of detector 2 in order to improve the angular resolution In this case the distance between lens and detector should be the focal length of the lens The focal length itself should be chosen in that way depending on the beam diameter that the focal spot is not too small The beam should still have a diameter on the sensor area of gt 50 um so that it hits all quadrants of the diode The gap between the quadrants of our standard 4QD measures 30 um Manual Beam Alignment System Compact version 6 October 14 2014 page 8 of 19 INNOVATIVE TREATMENT SOLUTIONS e Figure 9d shows a variation of 9c where both detectors are placed behind the same mirror A lens is placed in front of one of the detectors in order to measure both the beam position and the direction at the same point e Figure 9e finally shows a different arrangement where the 4 axes system is used as two 2 axes systems 1 e the two stages of the controller are used to separately stabilise two independent beam lines detector 2 application a detector 1 actuator 2 actuator 1 laser beam Figure 9a Typical sequence of
21. or one actuator is included in delivery additional or other cables on request x y position cable 2 cables 2 m other lengths on request Notes 1 A description of the sample amp hold circuit is given in a separate appendix Additional sample amp hold circuit to fix the laser beam position during laser off times 2 In case the beam diameter is larger than 6 8 mm a lens in front of the detector can be used For larger beam diameters adapters for 1 5 2 or other mirrors are available on request see also figure 13b in section 6 2 3 UV and IR detectors are available on request They may have differing dimensions and detection areas As an alternative to the 4 QDs we also offer PSDs These can have different dimensions and sensitive areas too Manual Beam Alignment System Compact version 6 October 14 2014 page 5 of 19 INNOVATIVE TREATMENT SOLUTIONS 3 1 Positioning accuracy The positioning accuracy depends on several parameters Optical distance between steering mirror and detector The accuracy is higher for larger distances Therefore a large distance should be chosen The first steering mirror should be placed close to the fluctuation source Beam diameter Having the same absolute change of laser beam position a smaller diameter leads to stronger power differences on the quadrants and therefore a steeper control signal That is why laser beams with smaller diameter can be positioned with higher accurac
22. range of steering mirrors Activate the controller module Start button switched ON green Active LED and LED on button shining and adjust the laser beam onto the detectors by means of manually tilting the steering mirrors until the four Range signals on the Piezo amplifiers are shining green Now the steering mirrors are operating in their linear range Manual Beam Alignment System Compact version 6 October 14 2014 page 11 of 19 INNOVATIVE TREATMENT SOLUTIONS ii Fine adjustment Obtaining zero position and full range of Piezo drives Inactivate the controller module Piezo drives are in zero position green Active LEDs are dark and adjust the laser beam by means of manually tilting the steering mirrors in that way that it hits the centres of the 4 QDs This can be done by reading out the x and y position outputs of the controller module or by observing the position display on the backside of the detector module The position outputs deliver a signal that is directly proportional to the deviation from the desired position You can easily display these signals on an oscilloscope The better the correlation of desired position and zero position the smaller the position shift after activating the closed loop control After these adjustments the system should show no fluctuations of laser beam position after the last mirror with detector when the controller is activated 5 Operation and safety features 5 1 Power level and position
23. stems With this set up the position of two independent lasers can be stabilised with one controller 4 4 Inputs and outputs The first steering mirror figure 2 is connected to the Actuator I output The second steering mirror is connected to Actuator 2 The connection of the detectors to the controller unit is made by a LEMO cable with a length of 4m and an adapter cable that splits the LEMO cable into four separate cables These cables are connected to the detectors according to the following rules The x and y lines have to be connected in accordance to the orientation of the detector housing If the detector is oriented in vertical orientation as shown in figure 4 the x line has to be connected to the x output and the y line to the y output If the detector is turned by 90 to a horizontal orientation as shown in figure 3 the x line has to be connected to the y output and the y line to the x output At the other end the LEMO cables of the detectors are connected to the respective 4QD inputs at the controller module Notes e The PKS steering mirror mounts can be mounted in two orthogonal orientations In the standard factory installation they are mounted and labelled in that way that the x axis drives the horizontal tilt and the y axis drives the vertical tilt If you change the orientation please take care that always the horizontal tilt must be connected to the x input and the vertical tilt must be connected to the y input of the control
24. wing section will then explain the single steps more comprehensively 1 Robust set up of optical components steering mirrors and detectors The centres of the detectors define the beam position The detectors can be placed directly behind mirrors Alternatively a small portion of the beam can be deflected to the detectors by means of a beam splitter 2 Cable connection First mirror with output Actuator 1 second mirror with Actuator 2 First detector with input 4OD1 second detector with input 4OD2 3 Switch on power supply switch on left side of housing Thereupon the four green Range LEDs will shine at the controller box 4 Adjustment of intensity on detectors by means of the potentiometer and if necessary exchange of optical filters In the best case 9 LEDs should be shining 5 Pre adjustment with non activated control stages Adjustment of the laser beam onto the detectors After this step no red LEDs of the position display LED cross should shine 6 Direction coding Activation of control stage 1 If red LEDs are shining on the controller box the switch position for x and y direction should be changed see section 4 6 7 Direction coding according to step 6 now for stage 2 8 Fine tuning for control stage 1 Deactivate both control stages Active LEDs do not shine Then follow the description in section 4 7 until the x and y position outputs are close to OV 9 Fine tuning for control stage 2 Activate sta
25. y Intensity The resolution of the detectors further depends on the intensity hitting the sensitive area This can be varied by an appropriate choice of optical filters and optimised electronically see also section 5 2 Repetition rate and pulse duration The controller bandwidth can be optimised for different laser parameters Higher bandwidths lead to a faster reaction and therefore higher accuracy in case of fast fluctuations In figure 8 the typical resolutions of the detectors are displayed The example shows that a resolution of better than 100 nm on the detectors can be achieved with an appropriate choice of parameters The angular resolution can be determined from these data with respect to the respective arm lengths resolution nm BV laser Beam diameter mm intensity W E es E Ww 0 1mm Figure 8 Resolution of a 4 quadrant diode irradiated by a red He Ne laser with different beam diameters and laser intensities The actuators are controlled with an analog signal so that the positioning is not restricted in separate steps The positioning accuracy of the Piezo elements are specified as lt 2nrad PKS and 4 nrad PSH Manual Beam Alignment System Compact version 6 October 14 2014 page 6 of 19 INNOVATIVE TREATMENT SOLUTIONS 4 Installation and operation 4 1 Brief step by step instruction The following steps shall assist you during the first startup of the beam stabilisation The follo
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