Review on methods of solving the refractive index-thickness coupling problem in digital holographic microscopy of biological cells

TL;DR

This paper reviews various methods to address the challenge of decoupling refractive index and thickness in digital holographic microscopy of biological cells, which is crucial for accurate biological and medical analysis.

Contribution

It provides a comprehensive overview of existing approaches to solve the refractive index-thickness coupling problem in digital holographic microscopy.

Findings

Summarizes key methods for decoupling refractive index and thickness.

Highlights the importance of accurate refractive index measurement for biological applications.

Discusses potential clinical and biological uses of refractive index data.

Abstract

Digital holographic microscopy is a thriving imaging modality that attracted considerable research interest in quantitative biological cell imaging due to its ability to not only create excellent label-free contrast, but also supply valuable physical information regarding the density and dimensions of the sample with nanometer-scale axial sensitivity. This technique records the interference pattern between a sample beam and a reference beam, and by digitally processing it, one can reconstruct the optical path delay between these beams. Per each spatial point, the optical path delay map is proportional to the product of the sample physical thickness and the integral refractive index of the sample. Since the refractive index of the cell indicates its contents without the need for labeling, it is highly beneficial to decouple cell physical thickness from its refractive index profile. This manuscript reviews various approaches of extracting the refractive index from digital holographic microscopy measurements of cells. As soon as the refractive index of the cell is available, it can be used for either biological assays or medical diagnosis, as reviewed in this manuscript.