Numerical Reconstruction Of The Sine Phase Grating Based On Digital Holographic Microscopy

Based on the digital holography and optics microscopic technology, by using numerical calculation method, digital holographic microcopy (DHM) reconstruct phase contrast images which provide quantitative measurement of phase distribution of microscopic object, it is a new method which reconstruct the amplitude and phase of microscopic object simultaneously. It has many characteristics such as high resolution and non-invasive, non-destructive, higher sensitivity and higher accuracy in measurement of tiny structures, which make digital holography a good application prospect in the field of microstructure measurement. In the paper, the microscopic sine phase grating is selected as a sample. we use digital holographic emersion program which designed ourselves to simulate the phase structure distribution of sine grating.The main research contents and features of this paper include the following aspects:1. Based on the Mach-Zender interference optical path, the off-axis digital holographic optical path system which record microscopic object is designed. By using the transmission recording system, the holograms of the grating are collected, and these holograms are stored in the computer.2. The paper works focused on the numerical reconstruction of a microscopic phase grating's phase distribution. Digital holographic recording and emersion program is completed. The microscopic sine phase grating is selected as a sample, holographic recording and emersion processes of the sample are simulated by the computer, the off-axis hologram is produced. By using the Fresnel approximate algorithm and fast Fourier transform, a single hologram is reconstructed numerically, calculation of the program is simple. In image processing, we apply the spectrum of filtering method to the program, the spectrum of zero-order image and twin image are filtered out, we get the high quality reconstruction image. Using unwrapping phase algorithm, the real phase of sine grating is achieved. This procedure has characteristics such as simple operation process, fast calculation speed, flexiblility etc.3. The numerical analysis to the phase distribution show that the program which we writed realize the perfect reconstruction of the sine phase grating's 3d structure, the phase information of the microscopic sine grating can be directly obtained, the program can be used for the phase distribution measurement of micro-object. 4. We set different reconstruction distances in the program to compare phase distribution of sine gratings. when reconstruction distance is 35mm, which compared with the former grating phase distribution diagram, the phase maximum of the both gratings are 6.283rad , and it doesn't produced phase distortion. The results show that only reconstruction distance completely equals to the recording distance, can the phase of the sine grating accurately reconstructed, in that way we can obtain the focus reconstruction image.5. By changing the sine grating cycle, we observe the emersion effect. Numerical simulation results show that with bigger grating cycle, the grating has more pixels, the reconstructed sine grating more smoother, the effect of the emersion image is better.At last, the computer simulation and the numerical analysis results which we completed show that it will provide meaningful reference and help for further research on the later digital holographic microscopic measurement.