Quantitative phase imaging with increased spatial coherence based on Fourier filtering

This Letter reports a method for tuning the degree of spatial coherence in an optical microscope. The method employs an amplitude spatial light modulator (aSLM) placed in the Fourier plane of the microscope. The aSLM displays a set of binary filters that blocks specific frequencies of the Fourier spectrum of the complex object field. It is shown that numerical processing of these filtered fields provides a final intensity with increased spatial coherence. Coherence tuning is used in a new hybrid phase reconstruction algorithm that employs the transport of intensity equation and an iterative phase retrieval technique. It is validated experimentally that this hybrid approach is able to retrieve the phase information with high resolution, and effective artifact noise suppression when employing at minimum two symmetrical defocused intensities and large sources.