Research On Methods For Improving The Quality Of Laser Beam Shaping

With wider application of laser,its unique hyperbolic propagation mode and gaussian wavefront limit its application.In holography,laser projection,laser printing and other fields,flat-top laser is required.To manipulate microscopic particles,laser catheters and tweezers are needed as tools,the annular laser beam is required.With the development of semiconductor technology,the need of real-time laser beam shaping becomes more urgent.BOE is small in size,light in weight,high in diffraction efficiency,wide in base material selection,easy to be integrated with other photoelectric devices,theoretically able to achieve arbitrary wavefront transformation,which is very suitable for laser beam shaping.In this paper,various kinds of optimization design algorithms are analyzed and stimulated in MATLAB.By comparing all the algorithm,the existing optimization algorithms are improved.In polar coordinates system,obtain high quality flat-top beam by using profile-smoothing & GS hybrid algorithm.In order to get annular output beam,an improved profile-smoothing algorithm is presented.These two algorithms could maintain high energy conversion efficiency without loss in uniformity.To meet technological requirements,this paper studies the fitting method for the precise phase of the optimization algorithm.This paper researches how the radius of BOE,sampling numbers and initial radius influence the phase fitting accuracy.The machinable BOE phase is obtained in Zemax.The evaluation index show the phase structure meets the design requirements.In order to utilize the real-time modulation characteristics of liquid crystal spatial light modulator(LCSLM),this paper analyzes the characteristics of its phase modulation mode,and proposes a method to simulate binary optical elements with LCSLM to realize real-time shaping of laser beam.In order to adapt to the approximate simulation of BOE phase by LCSLM,a hybrid algorithm based on the phase mixture algorithm(PMA)and profile-smoothing algorithm is put forward,reducing mean square error and uniformity of output beam at the same time.Using the phase-modulation characteristics of liquid crystal spatial light modulator(LCSLM),an experimental optical system is built.The input gaussian laser beam is shaped to flat top circular beam and rectangle beam respectively.The top beam uniformity and mean square error of the output beams received by CCD are less than 5%,and the energy concentration is higher than 90%.This mehod is proved to be a real-time,controllable and efficient laser beam shaping method.