Demystifying speckle field quantitative phase microscopy

TL;DR

This paper clarifies how dynamic speckle illumination enhances quantitative phase microscopy by enabling interference with flexible optics and large optical path differences, thus broadening its biomedical imaging applications.

Contribution

It provides a comprehensive theory and experimental validation of DSI in QPM, facilitating its use with non-identical objectives and large OPD ranges.

Findings

DSI enables interference with different objective lenses without loss of contrast.

Interference fringes are maintained over large optical path differences.

Theory supports wider adoption of DSI in biomedical imaging.

Abstract

Quantitative phase microscopy (QPM) has found significant applications in the field of biomedical imaging which works on the principle of interferometry. The theory behind achieving interference in QPM with conventional light sources such as white light and lasers is very well developed. Recently, the use of dynamic speckle illumination (DSI) in QPM has attracted attention due to its advantages over conventional light sources such as high spatial phase sensitivity, single shot, scalable field of view (FOV) and resolution. However, the understanding behind obtaining interference fringes in QPM with DSI has not been convincingly covered previously. This imposes a constraint on obtaining interference fringes in QPM using DSI and limits its widespread penetration in the field of biomedical imaging. The present article provides the basic understanding of DSI through both simulation and experiments that is essential to build interference optical microscopy systems such as QPM, digital holographic microscopy and optical coherence tomography. Using the developed theory of DSI we demonstrate its capabilities of using non-identical objective lenses in both arms of the interference microscopy without degrading the interference fringe contrast and providing the flexibility to use user-defined microscope objective lens. It is also demonstrated that the interference fringes are not washed out over a large range of optical path difference (OPD) between the object and the reference arm providing competitive edge over low temporal coherence light sources. The theory and explanation developed here would enable wider penetration of DSI based QPM for applications in biology and material sciences.