Reflective common-path digital holographic microscopy with partially coherent illumination

Holograms captured by digital holographic microscopic systems that use high-coherence lasers as light sources are heavily influenced because of coherent noise. The contrast of interferograms will be affected although coherent noise can be suppressed by using short coherence light sources. This paper develops a reflective common-path digital holographic microscopy (DHM) combined with partially coherent illumination. The light is scattered by a rotating diffuser and coupled into a multimode fiber, which form into an extended light source. After passing through an imaging system, the designed blazed grating generated by spatial light modulator (SLM) works as a polarization point diffraction plate at the Fourier plane, which has a circular area playing the role of a reflective pinhole at the position corresponded to the image of the multimode fiber. Being benefit from the polarization-selective modulation property of the particular blazed grating, polarization directions of diffracted component and non-diffracted component are modulated to be orthogonal. Because of the common-path configuration, the length of the object and reference path is equal and high contrast polarization phase-shifted interferograms are captured by polarization camera. Quantitative phase images are further obtained. A resolution target and a standard step plate are measured with the proposed system. The result of the resolution target shows that the lateral resolution is 715nm at least, which is higher than the reference method and close to the diffraction limit. Otherwise, the measured height of the standard step plate is 92nm and has only 4.76% deviation from the actual height, which represents high vertical resolution.