Speckle-free quantitative phase microscopy using pseudo-thermal light source for label-free imaging of biological cells and tissues with high temporal phase stability and spatial phase sensitivity

摘要

Quantitative phase microscopy (QPM) is a label-free imaging technique to quantify various biophysical parameters, suchas refractive index, optical thickness, cell dry mass, and dynamic membrane fluctuations. Accurate determination of theseparameters requires the use of a QPM system with high temporal phase stability and high spatial phase sensitivity. Wereport a QPM system based on a common-path interferometer with high temporal phase stability and high spatial phasesensitivity. The proposed QPM system is highly temporally stable, compact and easy to align and implement. Theinterference pattern can be obtained quickly even with a low coherent light source. In order to realize high spatial phasesensitivity, we used partially spatially coherent (pseudo-thermal) light source for illumination. Due to the partial spatialcoherent nature of the light source, a speckle-free interferogram/hologram is recorded over the entire field-of-view. Twotypes of speckle free QPM systems are implemented using common path Fresnel biprism as well as lateral shearinginterferometers. A Fresnel biprism is used in the self-referencing mode, thus offering the advantage of no optical powerloss in addition to high temporal stability and the least speckle artifacts. Furthermore, it is very easy to implement, as thesystem completely replaces the need for spatial filtering at the source end as well as for the reference beam generation. Inanother configuration, we used a lateral shearing interferometer. The scattered light from the object is collected by themicroscope objective lens and passes through a 4mm thick optically flat parallel plate to generate the interference pattern.Phase maps of human RBCs are reconstructed and the results are compared for fully and partially coherent lightillumination.