Optimizing three-dimensional point spread function in lensless holographic microscopy

In a number of previous studies on light focusing, the asymmetric axial intensity distribution with intensity peak shifted away from the paraxial focal plane was demonstrated for lenses working with a low Fresnel number. Here, the axial asymmetry of the three-dimensional point spread function (PSF) and the aberration effects are examined in a magnified phase-shifting holographic imaging achieved by the mismatch of reference and reconstruction waves. In the analysis, an optimal combination of experimental parameters and the range of applicable lateral magnifications are found for which the axial asymmetry of the PSF is not apparent and the aberration effects are acceptable. The focal shift and the axial asymmetry of the PSF and the effects of holographic aberrations are evaluated by approximate quantitative criteria whose validity is verified in exact numerical models and experiments. The optimal design of in-line holographic geometry is demonstrated by reconstructing the three-dimensional PSFs and the image of the resolution target recorded in the experimental setup using a spatial light modulator.