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1、MODULATORS FREQUENCY SHIFTERS LOW RESOLUTION DEFLECTORS Isotropic InteractionOperating ManualP1P#For further information, contactAA Sa Opto-Electronic DivisionTechnical Customers1 ServiceTel : +33 (0)1 76 91 50 12Fax : +33 (0)1 76 91 50 31CQiiaiitaZA.390Email : salesaafrAA Sa 18? rue Nicolas Appert

2、91898 ORSAY FranceTel: +33 (0)1 76 91 50 12- Fax : +33 (0)1 76 91 50 31 一 QUANTA TECH 116 West, 23rd Street Suite 500 New York, NY 10011 USAP#IMPORTANT3P2IMPORTANT3GENERAL PRECAUTIONS4Mechanical Precautions4Electrical Precautions4Optical Precautions4Installation and Adjustment Precautions4AO PRESENT

3、ATION5SYNOPTIC OF THE MODULATION SYSTEM5DESCRIPTION OF THE MODULATOR5MECHANICAL DRAWING5TO START OPERATION6ADJUSTMENT OPTIMIZATION7Acousto-Optic Efficiency7Acousto-Optic Rise Time8DIF冋CULTIES AND PROBLEMS, FAQ9TERMINOLOGY10FC7P0NK：AA Sa 18? rue Nicolas Appert 91898 ORSAY FranceTel: +33 (0)1 76 91 50

4、 12- Fax : +33 (0)1 76 91 50 31 一 QUANTA TECH 116 West, 23rd Street Suite 500 New York, NY 10011 USACQiianLu2A.380P#IMPORTANTThis operating manual is related to most of our products with Isotropic interaction. This includes AO Modulators, Frequency shifters and low resolution deflectors.To know its

5、specific characteristics (positioning, polarization, optical aperture, performanee), please refer to the information and test sheet of your modulator.This operati ng manual has been writte n in order to help for the in stallation of your AO comp on ent. Read this manual entirely before using, and ke

6、ep it n earby you when using the AO comp orient.Please read the Erreur! Source du renvoi introuvable. (page 4) before beginning the Erreur! Source du renvoi introuvable. part (page Erreur! Signet non defini. to 7). If you meet some difficulties with the installation of your AO component, please refe

7、r to the Frequently Asked Questions (page 9). For any question about the Acousto-Optic definitions or general purpose, refer to the last part, Erreur! Source du renvoi introuvable. (page 10).Thank you for the confidence in A&A Opto-Electronic 一 Hope to see you soon on our web pages .Please do not he

8、sitate to contact A& for further information:AA Opto-Electronlc DivisionCustomers1 ServiceTeL: +33 (0) 1 76 91 50 12Fax.: +33 (0)1 76 91 50 31E-mail: salesa-a.frGENERAL PRECAUTIONSMechanical Precautions/ Note that any strong mechanical shock can lead to irreversible damage on the component and parti

9、cularly on the crystalv For the products with fixation from the bottom part: take care with the length of the screws Too long screws may destroy the crystal.Electrical Precautionsv Do not force on the connectors7 Never disconnect the connectors while power supply is ON.Optical PrecautionsWindows Cle

10、aningv Dust on optical windows can be responsible for irreversible damage on the coating (especially il you use high power) Use the component in a clean environ me nt as much as possible 7 To clean up the optical surfaces: use a soft Q-tip. First, clean it with pure ethanol, then with acetone Most o

11、f AO comp on ents use soft materials and need careful cleani ng.v “Oily stains should be removed immediately to avoid irreversible marks.Installation and Adjustment PrecautionsAll of these specifications values are indicated on the test sheet of your AO comp on ent: Please refer to itLaser Power Den

12、sityv Check the maximum value specified for the give n AO comp orient, otherwise irreversible damage could occur.Laser Polarizationv Make sure that the specified optical polarization is correct to have an optimum AO efficiency (random, circular, perpendicular or paral el to the base 一 depending on t

13、he component).Optical Aperturev Holes in the housing of the modulator are larger than the specified optical aperture The AO component will need to be adjusted, using slight translations perpendicular to the laser beam, in order to get the beam traveling through the correct area of the crystal and to

14、 maximize the efficienc y.v Do not focus the laser beam on the AO cover.Incidence Anglev Make sure that the position of the AO component corresponds to the specified value of the incidence angle in order to optimize the efficiency.Warning: Any disassembling of your AO component makes the guarantee n

15、ull and void!AO PRESENTATIONLaser beam passing through an acousto-optic modulator, driven by an RF power, is diffracted into a single 1st orderf). Un der a specific in cide nee angle (bragg) the diffracted laser beam in tensity can be con trolled by the RF power. For low RF power, the diffracted las

16、er intensity is proportional to the Radio Frequency power.Each time we will speak about Modulator, you can replace by Frequency Shifter or Lowe resolution Deflector.C): This interaction can be possible if several parameters are respected (Bragg interaction).SYNOPTIC OF THE MODULATION SYSTEMAO connec

17、ted to the driver (Drive RF power： Voltage control)DESCRIPTION OF THE MODULATORThe principal elements of your AO component are represented in the drawing below.1 - Cover2 - Optical aperture3 - RF connector4 一 Fixation hole (threaded hole)5 - Bragg hole (cleared hole)(Refer to the Interface C) of you

18、r component)6 - Base Plate(: On the back of the test sheetMECHANICAL DRAWINGEach product may have a different mechanical drawing which can be provided by AA. This mechanical drawing states with accuracy the outer dimensions, the fixation holes and the optical axis.TO START OPERATIONIt is recommended

19、 to operate the AA Modulator with its associated AA RF driver, which is optimized at factory to get the highest performanee youre your AO component.Please refer to the AO test sheet to know the maximum RF power you need to operate your deviceFor the first installation, remove the protective tape on

20、the two apertures (IN & OUT) of the AO cover (D). IN and OUT are specified on the faces, when it has an importance and consequence on the performances of the component.For your safety and the safety of your modulator, do not install the modulator while the LASER is ON. Use a mechanical shutter or sw

21、itch off your laser during this procedure, especially for high power lasers.Now, you are ready to begin the installation of your AO component.OperationWhat do you do?CommentsInstall the AO component, so that the laser beam enters trough the IN face and by the optical aperture ()at its centre under t

22、he incidence angle, fFig. 1: Observations of the 0 order beam；on a black screen.Laser 532nm through an MT. 110Sbght rotationsScrew the AO component by using the fixationholes ()0 Fixation holes Make sure the laser beam diameter is lower than the given active aperture of the AO component, and its pow

23、er lower than the maximum power tolerated by the AO component.Typically: Beam Diameter 0.7x Active Aperture.To find quickly the optimal incidence angle, install the AO component near the auto-collimation (the reflexion does not pass inside the laser cavity but just dose). Then turn the AO component

24、to the incidence angle value indicated on the test sheet of your AO component.If you fix your AO component you will have less difficulties to proceed the following steps, and your product will be protected and “secured： Watch out for the screws length. Please refer to the test sheet to get the maxim

25、um authorized length. Screws that would be too long could damage the crystal.Check that the input laser polarization is conform to the base plate ()“ o ” orderInadent BeamG) A wrong input polarization will decrease the performances of the AO components and will lead to unexpected effects(Please refe

26、r to the test sheet of your component.)Connect the RF Output of your driver to the 41RF Connector ()of the AO component with the provided RF cable.Connect the RF Input of your driver to the control source (Signal generator, Power supply, PC Board.)Switch the RF driver on.Fig. 2: Diffraction of the l

27、aser beam through the AO component.2 Order广 Order0 Orderr1 Order IFig 3: Observation on a screen of the diffraction with a 532nm laser for a MT. 1100 Make sure that the delivered RF modulation output signal is compatible with the AO component (frequency and maximum voltage). When the RF signal is ap

28、plied to the AO component, the laser is diffracted as shown in Fig.3.G) Please note that in some cases (depending on your component) you can see several diffraction orders, but their intensity remains weaker than the first order. The angular sketch depends on your AO component. The first order can a

29、lso be positive or negative Please note that in order to give general information we never precise a sign for the first order in this manual. It doesnt correspond with your obsegtion?* Please refer to the Erreur! Source du renvoi introuvable. part (page Erreur / Signet non defini.)ADJUSTMENT OPTIMIZ

30、ATIONAcousto-Optic EfficiencyADUSTING POSITION OF THE AO DEVICEThe aim of this adjustment is to optimize the position of the AO comp on ent, by measuring the level of the output optical sign al. It requires the followi ng comp onents of measureme nt: photo-detector con nected to an oscilloscope O In

31、 stall a photo-detector on the H1S,W diffraction order (*) of the laser beam. Connect the photo-detector with an oscilloscope Check the level indicator on the oscilloscope, corresponding to the received laser intensity, stays in the linear part of the photo-detector. Adjust the in put laser in ciden

32、ce angle with a slight rotation of the AO comp orient to get the maximum inten sity in the 1st diffraction order. Adjustments can be done by handf thanks to rotation-translation stages, or thanks to the Bragg hole () for higher accuracy. This rotation can be positive or negative depending on the mod

33、el and on the shifted frequency. Please refer to the test sheet of your AO component to get this specification. Optimize the efficiency in the 1st diffraction order at the end in associating slight translations and rotations of the AO comp orient.INPUT POLARIZATIONThe aim of this adjustment is to op

34、timize the laser polarization, by measuring the level of the output optical signal in First order. It requires the following measurement system: photo-detector connected to an oscilloscope O Install a photo-detector on the Hlst,f diffraction order (*) of the laser beam. Connect the photo-detector wi

35、th an oscilloscope. Check the level indicator on the oscilloscope, corresponding to the received laser intensity, stays in the linear part of the photo-detector. Adjust the laser polarization with slight rotation of the laser to get the maximum intensity in the 1S， diffraction order.RF POWERIf an in

36、creasing RF signal power allows a better efficiency, but when the optimum RF signal value is exceeded, the efficiency decreases, because the conditions for an optimal Acousto-Optic interaction are either not observed.广 order AO Efficiency versus RF PowerAcousto-Optic Rise TimeOPTICAL SET-UPTo decrea

37、se the AO rise time (Tr) of your AO component, reduce the beam diameter (0): T = 0, with p a constant and v the acoustic velocity.vChoose the beam diameter to calculate the necessary focal length, use the following relation in function of theFJl4desired beam diameter (0):0 = a, with a a constant dep

38、ending on the beam profile (= for TEMOOV7tbeams, in Gaussian diffraction limited approximation)Precaution:Calculate the minimum rise time corresponding to the minimum beam diameter specified in【he test sheet ol your AO compone nt. In fact, if the beam diameter is too small, the laser beam diverge ne

39、e (DIV0) will be too large So there will be an incorrect matchi ng betwee n the laser beam diverge nee (DIV0) and the acoustic diverge nee (DIVA), which will lead to an output elliptic beam associated to an AO efficiency loss.C) Whew is the 卢 diffraction order? : 1 -Switch the RF signal off. 2丄ocate

40、 the diffracted laser beam (its the 0 order). 3-Switch the RF signal on. 4-Several orders appear. 5-Refer to the test sheet to know the position of the 1st order compared to the 0 order (at left or at right).DIFFICULTIES AND PROBLEMS, FAQYou may have some difficulties, while operating your AO compon

41、ent, to obtain the following diffraction figure:2 OrderF Order0 Order广 Order IObserv戲ton on a screen ot (he dtftracbon wth a 532nm laser for a MT.110Please, check at first the different values (incidenee angle, polarization, wavelength, frequency control ) in dicated on the test sheet of your AO com

42、p on ent.To proceed quickly, the following chart identifies some of the most frequently asked questions. We suggest some possible solutions and offer recommended replacement procedures.If your problem is not described below or if these explanations do not answer your needs, then please contact AA Cu

43、stomers1 Service.ProblemObservationPossible Cause and CorrectionNo light at the AO component output Laser Power Supply is not functioning. Laser Beam does not enter by the IN face of the AO componentLaser beam output diameter varies Laser Power is too high. Please refer to the test sheet, to get the

44、 maximum value supported by the AO component.Efficiency Loss at the AO Component Output (compared to the value specified in the test sheet) Laser Beam does not enter by the IN face of the AO component The laser polarization is not appropriated to the AO component. Please refer to the test sheet to k

45、now which polarization to use with the AO compone nt.d) The current which corresponds to the couple command of Tension / command of impedance is not appropriated to the product. Check the values (indicated on your Test Sheet) compare them which the piloting signal.Truncated spots (top and bottom) La

46、ser Beam is not centered on the optical aperture. Centre the laser (or the AO component) along the horizontal and the vertical axis. Laser Beam Diameter is too high. The laser beam output is truncated. Please refer to the test sheet, to get the maximum value for the AO component The laser beam does

47、not enter the crystal under the appropriate angle. Rotate the AO component to place it under the incidence angle specified on the Test Sheet of your product.Very scattered Laser Beam Outputcatterenirrusepot Oily atnina” rpmAin nn thp optical face mnd thfi Output 1Rpam iascattered. First, clean up th

48、e optical surfaces by using a soft Q-tip with pure ethanol, then with acetone.Elliptic Laser Beam OutputElliptic spots The laser beam diameter is too small. Enlarge the laser beam diameter. To know what is the minimum tolerated diameter, please refer to the Test Sheet of your AO component. The modul

49、ation is too fast for the component. Decrease the modulation speed. Please refer to the Test Sheet to get the exact value.The modulation speed is not sufficient (as quickly as the one indicated on your Test Sheet) The cunrent which corresponds to the couple command of Tension / comma nd of impedance

50、 is not appropriated to the product Check the values (indicated on your Test Sheet) compare them with the piloting signal. The laser beam diameter is too small. Increase the laser beam diameter with an expander, for example. To know what is the minimum tolerated diameter, please refer to the Test Sh

51、eet of your AO component. The detectors respo nse time is Ion ger than the modulati on speed. Please refer to the characteristics of your sensor to have its rise time. Do not use a T connector. It disturbs the signal (loss noise.)The deviation angle doesnt correspond with the one which is specified

52、on the Test Sheet (position and/or value) According to the model of the AO component (frequency, wavelength.) the Acousto-Optic interaction is more or less sensitive to the incidence angle between the laser beam and the AO component. Rotate the AO component to obtain the appropriated configuration.T

53、ERMINOLOGYParameterDimensionDEANTTION入mOptical Wav刨ength (air)fHzbght Frequencyni, ndIncident and Diffracted Crystal Indexeskukdm1Optical Incident and Diffracted Wave VectorAmAcousbc WavelengthKm1Acoustic Wave VectorFHzAcoustic / Drive FrequencyVm/sAcousbc VelocityPWAcoustic PowerPhIVRF Drive PowerV

54、rfVRF Dnve Voltage (defined by ms or /pp)VconVExternal Control Voltage of the RF Driver (Vri)looAIncident Optical IntensitykAOutput Optical Intensity at the 0 OrderhADiffracted Optical Intensity at the OrderDmOptical apertureT.sAccess TimeTrsAO Rise TimeFmHzModulation Frequency6djoSeparation AngleTO

55、ptical TransmissionnAO EfficiencyKEYWORDDEFINITION / COMMENTS / FORMULAAC0UST0-OPTIC INTERACTIONWhen an acoustic wave propagates in the Bragg cell, it generates a perturtoation of the refraction index in the cell. When the matchi ng phase is successful, the light is diffracted through the acoustical

56、 ” grating (with a grating step corresponding to the acoustic wavelength): Ay where v： the acoustic velocity and F: the acoustic frequency.The theory of the momentum and energy conserzations (for the incident light 他 f). the diffracted light 他 and the acoustic signal (K. F) allows to obtain the foll

57、owing expressions:kd =k jK with lkj2xn从 /kd/*2mA and /k/*2F/vFor Isotropic Interaction: n：=n(jn /k/= /kd/. fd = f F0M AND0!81 ORDERSThe P” and H1s,* orders are respective!y. the direct beam through the AO component, and the beam deviated by acoustic diffraclion grating.Output PolarizationIn the anis

58、otropic interaction, a flip of the incrden: polarization is produced depending on the difference of the material refraction index.In the isotropic interaction. the output polanzation is identical to the mcidenl polanzation (ni=na).Optical Transmission (T)The optical transmission is the rabo between

59、the Ight intensity at the output of the AO component (b) and the light intensity of the incident laser beam (loo): T Carrer Frequency(Fc)The carrier frequency allows to drive the AO component. To generate an AO interaction, the following relation must be v 2yx$in% respected:，厂=:.Drive Power (P韵The d

60、rive power is the electrical power delivered by the RF driver and sent to the AO smponent to drive the light output intensity.AcoustoOptic Efficiency(n)The AO efficiency is the ratio between the intensity in the 1 diffracted order (h) and in the 0 order (Iq):7y-sin2(7卩好)with c:a constantACCESS TIME

61、(TJThe access time is the time for the acoustic wave Q cross the optical aperture (D) of the AO component:7L =VACOUSTIC POWER (P)The acoustic power is proportional to the RF drive power P a x . with (a 1) a transformation factorAO RISE TIME (Ta)The AO rise time is the time for the AO efficiency to increase from 10% to 90%:八-wrth D: the beam diameter considering a pulse dnve signal and a Gauseian laser beamMODULATION FREQUENCY (F.)()4XNaturally linked to rise time: F. -j