Edge contrast enhancement of Fresnel incoherent correlation holography (FINCH) microscopy by spatial light modulator aided spiral phase modulation

Digital holographic microscopy (DHM) is one of the most effective methods in imaging the weakly-scattering objects, such as small colloidal particles and most biological cells. Compared to phase contrast and differential interference contrast microscopy, DHM cannot only visualize but quantify these phase objects. In this work, a spiral phase modulated FINCH microscope was implemented. The core of the system is an in-line incoherent interferometer composed of a spatial light modulator (SLM) and a charge-coupled device. In order to enhance image contrast, the SLM was space-division multiplexed by a helical lens and a conventional lens. To study the properties of this vortex imaging system, the precise mathematical model of the Point Spread Function (PSF), which describes the intensity distribution in digital image of the system’s response to a point source, is determined for the first time from the view of wave optics. The experimental 2D PSF agrees well with that of simulated one. When the system is used for biological microscopic imaging the enhancement of edge contrast and the enlargement of field of view are obtained without loss of resolution.