Highly stable wide-field common path digital holographic microscope based on a Fresnel biprism interferometer

Abstract

Quantitative phase imaging (QPI) of biological cells and tissues is an important technique useful in the determination of many biophysical parameters such as morphology, refractive index, thickness, cell dry mass, hemoglobin concentration, etc. Off-axis digital holography has been ideal for the QPI of microscopic specimens, but it has lower temporal stability compared to on-axis and common path digital holographic microscopes, which offer higher temporal stability. In this paper, we present a very simple, easy to align yet highly stable common path digital holographic microscope based on a Fresnel biprism interferometer. The system uses a biprism to divide the incoming beam into reference and object beams without the loss of optical power, unlike diffraction phase microscopy. Two methods are proposed, one by utilizing the spatial filtering mode and the other by the self-referencing mode. It offers the advantage that the reference beam can be easily created simply by translating the object in the focal plane of the microscopic objective or by spatially filtering one of the object beams in the Fourier domain. The proposed setup offers no power loss and a high phase stability of approximately 0.006 rad (6 mrad) without using any vibration isolation. The experiments on industrial and biological samples are reported demonstrating its application both for static and dynamic samples.