Research On The Beam Auto-collimation Technology Based On The Defocus Grating

Because of the high brightness, good direction and stability, laser beam has beenwidely used in many applications, such as hyperfine machining, laser medicine, laserphototypesetting, and etc. Unfortunately, during the production and transmission of thelaser beam, there exist displacement drift, angle drift and random drift, which are causedby the change of the cavity shape and the transmission environment. The magnitude ofthe laser beam’s drift is about10-4～10-6rad. The drift restricts the collimation precisionof laser beams and limits their application fields. To restrain the wobble of the beam andimprove the pointing stabilization, a new beam alignment technique based on thedefocus grating is proposed and studied theoretically and experimentally in this paper.The main contents of this thesis are as follow:(1) The relationship between the location change of the diffraction spot and thelaser beam’s drift has been built based on the approximation of Huygens-Fresnelprinciple and the imaging principle of the defocus grating.(2) A model of the beam transmission has been built by using the Matlab software.The relation between the key parameters of the defocus grating and the biggest driftvalue which could be detected has been simulated and analyzed. The best designparameters have been given under the lab conditions.(3) The beam alignment strategy has been proposed, based on the measurementprinciple of beam drift. The working principle and the technical criterion have beenintroduced. The key technique has been studied and solved. We have given detailedanalysis about the experiment and the feasibility of this strategy has been provedexperimentally. The experiment results show that the beam disturbed by the static driftor the quasi static drift have been collimated successfully. The remained displacementdrift is equal to0.11mm, and the remained tilt drift is equal to12".