Research Of Ultrafast Laser Shaping Technology Based On Spatial Light Modulator

Ultra-fast laser generally refers to the laser beam with single pulse width below tens of picoseconds,which has the advantages such as low pulse width,high peak power density,small heat-affected zone and high processing precision.Ultra-fast lasers enable cold processing of materials.Ultrafast laser processing technology has been widely used in 3D printing,laser direct writing,material surface modification,holographic optical tweezing,two-photon polymerization,meta surface processing,and medical treatment.However,ultra-fast laser processing technology suffers from low processing efficiency,poor laser energy utilization,and a single optical field structure,which limits its adaptability to a variety of different processing needs.To address the above problems,this thesis combines optical field modulation technology,computational holography and image processing technology to design several schemes for shaping the picosecond laser based on liquid crystal spatial light modulator(LC-SLM).The main contents of this thesis are as follows:(1)We introduce some basic theories such as the beam shaping method based on scalar diffraction theory,the basic principle of computational holography,the calculation method and production method of phase diagram and computational hologram,and the principle and method of light field modulation by reflective liquid crystal spatial light modulator.(2)In order to improve the processing efficiency and laser energy utilization of the picosecond laser,we built an optical system based on a reflective liquid crystal spatial light modulator for shaping the beam of the picosecond laser.This thesis describes the factors that affect the quality of beam shaping and compares several different zero-order beam elimination methods.Based on the current common laser beam splitting and shaping algorithms such as iterative Fourier algorithm,global algorithm and hybrid algorithm,we designed a hybrid algorithm based on real-time feedback to improve the uniformity of the picosecond laser beam splitting,and verified the practical effect of the proposed method by laser processing experiments.(3)We present the application of vector beams in laser processing and analyze the influence of the laser’s polarization state on the processing results.Based on the liquid crystal spatial light modulator,we have realized the dynamic regulation of the polarization state of the focused laser spot and verified the superiority of the vector beam compared with the linearly and circularly polarized beam for 304 stainless steel drilling by laser processing.