Research And Application Of Digital Holographic Measurement Based On Spatial Light Modulator

Digital holography is a non-destructive and efficient method of optical inspection,as the three-dimensional shape of an object can be recovered from a single frame.However,for objects to be measured with abrupt phase changes,the detection results suffer from discontinuous phase information and inaccurate phase unwrapping.Therefore,how to achieve effective phase compensation,improve the accuracy of digital holographic phase reconstruction,becoming the current research hotspot.Based on the analysis of the basic theory of digital holography and the study of the phase modulation characteristics of liquid crystal spatial light modulators,this paper constructs a Mach-Zehnder type digital holographic phase compensation measurement scheme based on liquid crystal spatial light modulators,and carries out experimental research on the application of wavefront correction and phase compensation.Its main research elements include the following three points.(1)Research on digital holographic measurement based on phase compensation.This paper describes the record and reproduction process of digital holograms,and gives a series of algorithms for pre-processing,phase reconstruction and phase unwrapping of digital holograms in detail.Based on the inherent electro-optical properties of liquid crystal molecules,the relationship between phase delay and intensity reflectance of liquid crystal spatial light modulators is constructed in conjunction with Jones matrix theory,and the relationship between phase delay and polarizing angle is simulated and analysed,providing a theoretical basis for the characterisation and application experimental research of phase modulation in the later paper.(2)Phase modulation characteristic and non-linear error correction of liquid crystal light is studied.In this paper,two phase modulation characteristic test systems are designed based on reflective liquid crystal spatial light modulators:the Teman-Green Interferometric System and the Fizeau Interferometric System.The experimental results show that the maximum phase modulation of the liquid crystal spatial light modulator is 1.956?and 1.932 ?,which proves that the two test systems have a high degree of consistency.Subsequently,this paper proposed a phase nonlinear correction algorithm based on reverse interpolation in a non-linear response problem of the liquid crystal spatial optical modulator.The correction results show that the non-linear error of the liquid crystal spatial light modulator is reduced from 8.5%to 1.75%.(3)Research on digital holographic compensation measurement method and application based on liquid crystal spatial light modulator.The modulated grayscale map of the optical system wave aberration is designed according to the Zernike polynomial,and the wave modulation function of the liquid crystal spatial light modulator is verified.On this basis,the experimental system for wavefront correction of planar flat crystals is designed.For planes with a diameter of 50 mm,it can effectively correct the pre-transmission wavefront deviation;Finally,a Mach-Zehnder-type digital holographic phase compensation application measurement system based on a liquid crystal space light modulator is constructed.Experiments show that the measured object phase depth can be compensated from 5 rad to 0.7 rad,which can effectively improve the phase reconstruction accuracy of the digital hologram.The digital holographic phase compensation measurement technology based on the liquid crystal spatial light modulator can realize the effective compensation of mutation phase,which provides a new idea and new way for digital holographic high precision phase reconstruction.