Extended Resampling of Subharmonic Atmospheric Turbulence Simulation Phase Screen Research
The simulation of wavefront distortion caused by atmospheric turbulence has been a key technique in the study of remote target imaging,light propagation in the atmosphere,large astronomical telescopes and the design of adaptive optical systems.The rapid generation of high-precision atmospheric turbulence phase screens is particularly important for studying the performance of remote target imaging and adaptive optical systems.At present,the most commonly used simulation method is the spectral inversion method based on fast Fourier transform.Due to the constraints of F ourier transform itself,the phase screen model generated by spectral inversion method lacks low frequency information.Turbulence energy is mainly concentrated in the low frequency region,and the commonly used subharmonic methods developed on this basis fail to adequately sample the low frequency region,resulting in energy leakage.In this paper,an extended resampling subharmonic method is proposed to rapidly generate the atmospheric turbulence phase screen,expand the original region,and divide it into four sub-blocks.Then,each sub-block is further divided into four smaller sub-blocks,and the extended low-frequency region is intensively sampled,and so on.With the continuous grid division,lower frequency components can be continuously added,the initial region of low-frequency compensation can be expanded,and a new sampling method for the low-frequency compensation region is designed.Based on the simulation with Kolmogorov theory,the error between the phase structure function and the theoretical value of the phase plate generated by setting different harmonic order is analyzed.The results show that when the subharmonic order is 11,the relative error between the phase structure function and the theoretical value of the phase plate generated by the extended resampling subharmonic method is 0.368％.Because the external field experiment is affected by environment,climate and other factors,the uncertainty is large,so it is necessary to build an atmospheric turbulence simulator in the laboratory for experiments.According to the results of the external field experiment,the telescope used in the external field experiment was scaled down,and the commonly used lens materials were used in the software to simulate and design the atmospheric turbulence simulator.Finally,the MTF curves of each field of view were close to the diffraction limit,and the Huygens point diffusion function had no obvious defects.According to the simulation results,the atmospheric turbulence simulator system was built in the laboratory for analysis.The system includes a light source,a target object,a front lens,a splitter prism,a liquid crystal spatial light modulator,an aperture,a back lens and a board level camera.The light emitted by the object passes through the refraction of the front group of lenses and forms parallel light in each field of view.After the beam splitting prism,linearly polarized light with polarization direction parallel to the experimental platform is formed in the transmission direction and incident on the surface of LCOS-SLM.LCOS-SLM can carry out phase modulation on the incident light by loading the atmospheric turbulence phase diagram on the computer.The light beam reflected by the LCOS-SLM is focused through the rear lens to form a telecentric light path in the image side,and the final image is imaged on the receiving surface of the board level camera.The results show that after loading the atmospheric turbulence phase screen generated by this method,the absolute error of the turbulence effect on image MTF and the turbulence modulation transfer function curve is small,the average error is 0.033 6,that is,the method can generate a high-precision atmospheric turbulence phase screen.
Atmospheric opticsAtmospheric turbulence phase screenSub harmonicPhase structure functionOptical transfer function
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