Study of the reconstructing methods of the digital off-axis lens-less Fourier transform hologram

In order to improve quality of reconstructed images,the common algorithms used to reconstruct digital holograms was studied by means of comparison.According to the theorems of holography and linear system,the reconstructing methods of the off-axis lens-less Fourier transform hologram by Fresnel diffraction formula and by the convolution method based on Rayleigh-Sommerfeld diffraction integral were studied through simulation.The results show that Fresnel diffraction formula is still correct within very short recording distance,although the traditional Fresnel approximate condition isn't fulfilled.The characters of the fast Fourier transform of the free space impulse response are different at different distance,so the quality of the reconstructed image by the convolution isn't perfect.For the microscopy by off-axis lensless Fourier transform holography,Fresnel reconstructing method is better than the convolution method.