Research On Digital Holographic Wavefront Reconstruction

A charge-coupled device is used to replace the traditional recording medium in digital holography,which can realize the wavefront reconstruction of digital holography by computer software,so as to realize the digitization and real-time of the holographic technology.Because of its advantages,digital holography has a great application prospect in many field,such as particle field detection,image kryptonite,high resolution microscopic imaging,etc.This paper focuses on the acquisition of high-quality digital holograms,the wavefront reconstruction of digital holography and the improvement of the quality of wavefront reconstruction.The main work is as follows:In terms of the acquisition of high-quality digital holograms,firstly,according to the sampling theorem and spectral separation conditions,the influence of the incident angle of the reference light and the recording distance on the hologram was given by theoretical analysis.That is,the maximum value of the reference light incident angle decreases as the CCD pixel size increases,and increases with the increase of the wavelength;the minimum value of the reference light incident angle is determined by the size of the object,the effective size of the CCD,and the recording distance.Besides,when the recording distance satisfies a certain range,and the positive and negative first and zeroth levels of the reconstructed wavefront are separated from each other,the detailed structure of the object can be recorded to the greatest extent.Furthermore,according to the theoretical results,the corresponding experimental structure was designed.The experimental results obtained are consistent with the theoretical analysis.In the reconstruction of digital holographic wavefront,the reconstruction distance of digital wavefront reconstruction was firstly analyzed theoretically.The wavefrontreconstruction distance is inversely proportional to the square of the digital hologram scaling ratio,whereas proportional to the recording distance.Furthermore,the digital reconstruction experiment was carried out.Detailedly,the digital reconstruction program was written by MATLAB software,and the digital reconstruction was realized.The digital reconstruction experiment confirmed that the relationship between the wavefront reconstruction distance and the hologram zoom ratio as well as the recording distance is consistent with the theoretical analysis.Secondly,the optical reconstruction of digital holographic wavefront was studied.The corresponding experimental optical path was designed,and the optical wavefront reconstruction of digital hologram was investigated experimentally by amplitude-type spatial modulator and phase-type spatial modulator.The size of the aperture makes the spot size of the illumination to the spatial modulator to be suitable,which can effectively reduce the influence of the diffraction spot generated by the structure of the spatial modulator on the wavefront reconstruction of the digital hologram;and for the phase type spatial modulator,the brightness of the reconstructed image of the digital holographic wavefront can be enhanced by adjusting the phase.In terms of improving the quality of wavefront reconstruction,the frequency domain filtering and interception of effective information were both studied as well as image processing methods.The results show that the frequency domain filtering can remove the interference of the zeroth-order and negative-level wavefront reconstructed images,and improve effectively the quality of the digital holographic wavefront reconstructed image.Appropriate interception of effective information,or variation of relative position of the effective information can reduce the influence of direct light transmission on the reconstructed image of the digital holographic wavefront to some extent.The obtained digital holographic wavefront reconstructed image and the image processing method can improve further the quality of the image edge.