Study On Diagnosing The Distorted Wavefront Of A Laser Beam By Radial Shearing Interferometer And Controlling It By A New Method

The diagnosis and control of distorted wavefront is a key issue in thefield of high power laser system, Which will directly decide the laser beamquality and the cost of a laser system. In this doctOral dissertation, a newresearch of the diagnosis and control of laser wavefront distortion hasbeen imPlemented. A cyclic radial shearing interferometer was used todiagnose the wavefront distortion of a laser system and an LCSLM(liquidcrysnd spatial ligh modulator) was used to control it. Some results havebeen summarized as follows:l. According tO the theory of scalar quanity diffeaction and the modelof the random Gaussian phase screen of low frequency wavefront, theeffect of the low frequency wavefront with different RMS gradient on thefocal sPot of a laser beam was stUdied. And a numerical simulation whichthe portion of the PSD(power spectral density) contributes to the tail of themain focal spot was studied too. -2. In order to accomPlish the eXtraction measuremellt of distOrtedwavefrOnt on specific plane of a laser beam, a CRSI(cyc1ic radial shearinginterferometer) based on relay imaging technique was built. TheeXPeriInental result on this CRSI shows it can used to test the spatial midand low frequency wavefront distortion.3. A new algorithIn to be used to recontrict the distorted wavefrontfrom itS CRSI ffinge pattem has been presented. It can be used to exactlyexPlain the CRSI funge pattem of an arbitrary wavefront. And theconvergence of this algorithm was analyzed too. The results of numericalcomplltaion and eaperiment show that our algorithIn is correct. Moreovef,the CRS interferogram of a step wavefront was exPlained. It shows that adisadvantag ekistS when a CRSI is used to measure a steP strUcture in awavefrOnt, but it is useful tO adjust a CRSI system with LCSLM.4.According to the didriction effect of an aPertUre, the spatialresolution of our CRSI was analyzed and the transform function of ourCRSI was calibrated by using the PSD method of a step wavefront. Andsome factOrs Which are associated with the accuracy of our CRSI wereanalyzed too. The relationship betWeen radial sheared ratio and theaccuray of ffos CRSI was investigated. Furthermore, the range ofmeasurement of it was pointed out. All the analysis shows that our CRSI1Ilcan be used to measure the spatial mid and low frequency wavefront distortion.5.Based on our CRSI and algorithm, the phase modulation characteristic of an LCSLM was measured. And the correction of a step wavefront produced by a step phase plate is accomplished successfully.6.According to the phase modulation characteristic of an LCSLM, arbitrary complicated wavefronts were modeled. The result shows that LCSLM can be use to test the wavefront sensors and controller if LCSLM has wider dynamic range and perfect optical quality.7.Based on our CRSI and algorithm and double LCSLM, an adaptive optical hardware system which c&n be used to model arbitrary complicated wavefront and the compensation of the wavefront can be accomplished was built. And according to the characteristic of a CRS interferogram of a step wavefront produced by an LCTV, the pixel-level calibration of this system is implemented. The control of the spatial mid frequency wavefront distortion was achieved based on our CRI wavefront sensing and LCTV wavefront correcting system.The results of our research show that CRS interferometer can be used to diagnosing the mid and low frequency wavefront distortion of a laser beam and LCSLM can be used to availably controlled it.