Research On Wavefront Phase Retrieval Method Based On Single Frame Focal Plane Image

The phase retrieval technique of wavefront is a method of reconstruction wavefront aberrations by using the information of two-dimensional intensity distribution of beam diffraction field.The traditional phase retrieval method based on single-frame focal plane image has the advantages of simple structure and energy concentration.However,this method has multiple solutions problem,that is,one far-field spot corresponds to multiple near-field wavefronts.At present,the phase diversity method is the most accurate phase retrieval method.However,this method needs to detect two or more far-field images by light splitting,so the device is complex and its application is limited.In order to solve the above problems,this paper uses two-dimensional spatial modulation technology to break the symmetry of near-field aberration,and proposes a single frame focal plane image retrieval method based on two-dimensional discrete phase modulation of Walsh function.Compared with the traditional phase retrieval algorithm,this method reduces the number of iterations,saves the running time of the algorithm,and can accurately reco nstruct the aberration to be measured.Then a phase retrieval method based on the Fresnel zone plate with mixed focal length is proposed.The structure of this method is simpler.By using two-dimensional micro machining technology,multiple focal lengths can be combined in different quadrants of a substrate.The focal plane information and defocusing information of some wavefront can be detected at the same time by the CCD target,and the wavefront can be accurately recunstructed by this combined information.The main contents of the paper are as follows:The theoretical models of lens wavefront transmission based on Fraunhofer diffraction and optical angle spectrum transmission are studied.By theoretically deriving the spatial and frequency domains of the discrete Fourier transform,the number of sampling points required for the uniform object space and image space coordinates is obtained.The experimental platform is built to verify the accuracy of the two optical transmission models applied to the lens far-field calculation.A single-frame wavefront reconstruction method based on Walsh function two-dimensional discrete phase modulation is proposed.The multi-solution problem of traditional phase retrieval method based on single-frame focal plane image is analyzed theoretically.Theoretical derivation and simulation verify the far-field intensity distribution of two-dimensional discrete modulation based on Walsh function.The results show that this method can break the symmetry of near-field wavefront aberration and overcome the multi-solution problem.The traditional GS phase retrieval algorithm and the wavefront reconstruction algorithm based on Walsh function phase plate modulation are simulated.The results show that the traditional algorithm is easy to converge to the local minimum value or false solution when recover the aberration,and the proposed method can recover the wavefront information more accurately after dozens of iterations.Taking the four-quadrant Walsh function modulator as an example,the system parameters affecting the reconstruction accuracy are studied.Accuracy analysis and experimental study of single-frame wavefront reconstruction method based on four-quadrant phase plate modulation are carried out.Firstly,the factors affecting the accuracy of the four-quadrant modulation wavefront retrieval method are simulated.Aiming at the low signal-to-noise ratio(SNR),a method of collecting the same far-field image twice by changing the exposure time of CCD,and then stitching the two images to obtain the far-field high-frequency information covered by noise is proposed.The design and fabrication of four quadrant phase plate are introduced,and the aberration measurement system of four quadrant modulation wavefront detector is built.The experimental results show that the four quadrant modulation wavefront detector can reconstruct wavefront aberration more accurately.A simpler wavefront reconstruction technique based on hybrid focal length Fresnel zone plate is proposed.Part of the focal plane information and part of defocusing information can be detected in the same far-field spot,and the far-field spot with special intensity information is generated.The proposed method is verified by simulation.The results show that this method has good retrieval effect for single-order Zernike aberration and random aberration.The factors affecting the measurement accuracy of this method are analyzed.The results show that the number of CCD bits has a more obvious effect on the aberration reconstruction precision.The influence of semiconductor process error on the imaging quality of Fresnel zone plate with hybrid focal length is also analyzed.It is proposed that the linewidth accuracy of Fresnel zone plate should be strictly controlled in the process of fabrication.