Extension of refocus depth range in digital holographic microscopy.

Digital holographic microscopy (DHM) suffers from a limited refocus depth range due to the employed microscope objective. The relationship between the refocus depth range of the DHM system and its optical parameters is studied theoretically and experimentally, and a method is proposed that combines wavefront coding with bicubic interpolation and extrapolation iteration to extend the refocus depth range. For obtaining a uniform point spread function on the refocus plane, a propagator kernel in numerical reconstruction is multiplied by a numerical logarithmic phase mask, and a deviation of the refocus distance is made. To improve the resolution of the refocused image, the size of the hologram is doubly enlarged. This approach can extend the refocus depth range from 0.9 up to 1.5 mm. This work provides important guidance for high-resolution imaging with a large refocus depth range in DHM.