Low-Coherence Shearing Interferometry With Constant Off-Axis Angle

Rongli Guo,Itay Barnea,Natan T. Shaked

doi:10.3389/fphy.2020.611679

Abstract

We present a wide-field interferometric imaging module for biomedical and metrological measurements, employing shearing interferometry with constant off-axis angle (SICA) that can work, for the first time, with a low-coherence light source. In the SICA module, the shearing distance between the interfering beams can be fully controlled without a direct relation with the off-axis angle. In contrast to our previous SICA module, here we use a low-coherence illumination source, providing quantitative phase profiles with significantly lower spatial coherent noise. Although a low-coherence source is used, we obtain off-axis interference on the entire camera sensor, where the optical path difference between the two beams is compensated by using a glass window positioned in the confocal plane. This highly stable, common-path, low-coherence, single-shot interferometric module can be used as an add-on unit to a conventional bright-field microscope illuminated by a low-coherence source. We demonstrate the advantages of using the module by quantitative phase imaging of a polymer bead, fluctuations in a human white blood cell, and dynamics of human sperm cells.

Highlights

Wide-field interferometric phase microscopy (IPM), called digital holographic microscopy, is a method that can render quantitative phase images of micro-scale samples by recording their complex fields [1,2,3,4,5,6]
We introduce a low-coherence shearing interferometry with constant off-axis angle (SICA) (LCSICA) module that allows single-shot quantitative phase imaging with both high spatial and temporal phase sensitivities, with highvisibility off-axis interference over the whole field of view
The shearing distance between the interfering beams is controlled by the axial distance of the diffraction grating, and is set to be large enough so that no overlap occurs with ghost images containing negative phase values

Summary

Introduction

Wide-field interferometric phase microscopy (IPM), called digital holographic microscopy, is a method that can render quantitative phase images of micro-scale samples by recording their complex fields [1,2,3,4,5,6]. Self-referencing interferometry includes, for example, τ interferometry [23, 33], flipping interferometry [24, 25], diffraction phase microscopy [27], shearing interferometry [28, 29], the quantitative phase imaging unit [30], quadriwave shearing interferometry [31] All of these interferometers have a nearly common-path interferometric geometry, and inherently have a higher temporal phase sensitivity than the conventional Michelson and Mach–Zehnder

Methods

Results

Conclusion