Correction of nonparaxial and misfocus aberrations in digital lensless Fourier transform holography

In digital lensless Fourier transform holography, performing inverse Fourier transform directly to the digital hologram for the numerical reconstruction of the object field requires two conditions. Firstly, the paraxial approximation condition must be satisfied in the recording process of the hologram, otherwise a nonparaxial aberration will be produced in the reconstruction process. Secondly, the distances from the object plane and the reference point source to the recording plane of the hologram must be equal, or else a misfocus aberration will be produced in the reconstruction process. The grayscale distribution of the digital lensless Fourier transform holograms recorded under the condition of nonparaxiality or misfocus is analyzed in theory, and corresponding numerical correction methods for nonparaxial or misfocus aberration are introduced, respectively. According to the actual recording conditions, if using proper correction factors for nonparaxiality or misfocus to multiply the grayscale distribution matrix of the recorded digital hologram, the influence of the nonparaxialty or misfocus can be removed. Accurate digital reconstructed image will be obtained by performing inverse Fourier transform directly to the corrected hologram grayscale matrix. The experimental results show that the introduced numerical reconstruction methods can well correct the nonparaxial or misfocus aberration and thus improve the quality of the digital reconstructed image in digital lensless Fourier transform holography.