Effect of partial spatial coherence of light on quantitative phase microscopy of biological samples: improved spatial phase sensitivity, space-bandwidth product, and high accuracy in phase measurement

Quantitative phase microscopy (QPM) has recently become indispensable technology for label-free quantitative analysis of various biological cells and tissues, such as, sperm cells, liver sinusoidal cells, cancerous cells, red blood cells etc. The key parameters controlling measurement accuracy and capability of QPM system depends on its spatial and temporal phase sensitivity. The spatial phase sensitivity of QPM is governed by coherence properties of light source and temporal stability depends on optical interferometric configuration. Most of the QPM techniques utilize highly coherent light sources like lasers benefited by their high spatial and temporal coherence, and brightness. But high spatio-temporal coherence leads to occurrence of speckle noise and spurious fringes leading to inhomogeneous illumination and poor spatial phase sensitivity. We have developed QPM systems using partially spatially coherent monochromatic (PSCM) light sources which guarantees high contrast interferograms over large field-of-view to increase space-bandwidth product of QPM system by ten-times and demonstrated ten-fold improvement in spatial-phase sensitivity and phase measurement accuracy compared to coherent laser light. By means of using PSCM with common path configuration we could also achieve ten-fold temporal phase stability. We have demonstrated advantages of PSCM based QPM in various industrial and bio-imaging applications. Experimental results of reduced speckle noise, free-from spurious fringes, spatial phase sensitivity using industrial objects are demonstrated and compared with highly coherent light using single mode fiber. Finally, phase map of biological samples is also presented with high accuracy in phase measurement. Thus, the use of PSCM light in phase microscopy, holography of realistic objects, i.e., industrial and biological samples leads to high accuracy in the measurement of quantitative information.