Control Of Beam Spatial Characteristics Based On Liquid Crystal Light Modulator

With the development of laser technology,laser is more and more widely used in various fields,such as laser radar,optical information processing,laser printing and other technologies.Different application fields need to use different characteristics of laser beam,which requires the control of spatial characteristics of laser beam on demand.Based on the liquid crystal light modulator,the fundamental mode Gaussian beam is converted into high-order Gaussian beams of different orders,such as Hermite-Gaussian beams and Laguerre-Gaussian beams.The main work is as follows :Firstly,the paper briefly introduces the research status of beam control technology at home and abroad,and discusses the advantages of using liquid crystal light modulator method.After determining the beam control scheme,the distribution and transmission characteristics of the fundamental mode Gaussian beam,as well as the basic characteristics of Hermite-Gaussian beam and Laguerre-Gaussian beam are described.Secondly,based on the Helmholtz equation and scalar diffraction theory,the physical essence of laser beam generation is discussed,and the spatial distribution of high-order Gaussian beam is numerically simulated by MATLAB software programming.Three fast algorithms for calculating Fresnel diffraction based on Fourier transform are introduced.Four phase recovery algorithms are briefly described.On this basis,an improved algorithm based on single Fourier transform and GS algorithm is proposed.The phase modulation characteristics of the reflective liquid crystal light modulator are measured by using the Twyman-Green interference optical path.The GUI interface data processing software is designed to analyze the intensity distribution of the interference fringes generated by different grayscale images.The offset of the interference fringes is obtained,and the corresponding relationship between the phase and the grayscale is fitted.In view of the nonlinear characteristics of liquid crystal light modulator in practical work,and the deviation between the phase modulation depth and the factory setting value,the cubic spline interpolation method is used to calibrate and compensate the phase modulation characteristic curve of liquid crystal light modulator.The Fresnel lens grayscale image of the phase-gray relationship before and after correction is made by liquid crystal light modulator.The comparison of the experimental imaging clarity before and after correction shows that the cubic spline interpolation method has good correction effect and reliability for the correction of SLM phase-gray relationship.Finally,an optical system based on liquid crystal light modulator to realize beam spatial characteristic control is built.The intensity distribution grayscale images of high-order HermiteGaussian beams and Laguerre-Gaussian beams of different orders are numerically simulated.The corresponding phase grayscale images are produced by improving the GS algorithm,and the phase grayscale images are loaded into the liquid crystal light modulator.The corresponding target beam is obtained by experimental output.The analysis and comparison of the output highorder Gaussian beams show that the similarity between the generated high-order Gaussian beam spot and the target spot is higher than 96 %,and the energy utilization rate is greater than 78.78 %.