Bright-field microscopy of transparent objects: a ray tracing approach

TL;DR

This paper presents a geometrical optics-based ray tracing method to model bright-field microscopy of transparent objects, enabling phase information extraction and potential object reconstruction.

Contribution

It introduces a simplified ray tracing approach that reproduces wave theory results and suggests new methods for quantitative phase imaging in bright-field microscopy.

Findings

Ray tracing reproduces paraxial wave theory results.

Two methods for phase information extraction are proposed.

Potential for reconstructing object morphology from bright-field images.

Abstract

Formation of a bright-field microscopic image of a transparent phase object is described in terms of elementary geometrical optics. Our approach is based on the premise that image replicates the intensity distribution (real or virtual) at the front focal plane of the objective. The task is therefore reduced to finding the change in intensity at the focal plane caused by the object. This can be done by ray tracing complemented with the requirement of conservation of the number of rays. Despite major simplifications involved in such an analysis, it reproduces some results from the paraxial wave theory. Additionally, our analysis suggests two ways of extracting quantitative phase information from bright-field images: by vertically shifting the focal plane (the approach used in the transport-of-intensity analysis) or by varying the angle of illumination. In principle, information thus obtained should allow reconstruction of the object morphology.