In this Letter, we demonstrate quantitative phase imaging of biological samples, such as human red blood cells (RBCs) and onion cells using narrow temporal frequency and wide angular frequency spectrum light source. This type of light source was synthesized by the combined effect of spatial, angular, and temporal diversity of speckle reduction technique. The importance of using low spatial and high temporal coherence light source over the broad band and narrow band light source is that it does not require any dispersion compensation mechanism for biological samples. Further, it avoids the formation of speckle or spurious fringes which arises while using narrow band light source.

We report multispectral phase-shifting interference microscopy for quantitative phase imaging of human red blood cells (RBCs). A wide range of wavelengths are covered by means of using multiple color light emitting diodes (LEDs) with narrow spectral bandwidth ranging from violet to deep red color. The multicolor LED light source was designed and operated sequentially, which works as a multispectral scanning light source. Corresponding to each color LED source, five phase-shifted interferograms were recorded sequentially for the measurement of phase maps, as well as the refractive index of RBCs within the entire visible region. The proposed technique provides information about the effect of wavelengths on the morphology and refractive index of human RBCs. The system does not require expensive multiple color filters or any wavelength scanning mechanism along with broadband light source.

In breast cancer, 20%–30% of cases require a second surgery because of incomplete excision of malignant tissues. Therefore, to avoid the risk of recurrence, accurate detection of the cancer margin by the clinician or surgeons needs some assistance. In this paper, an automated volumetric analysis of normal and breast cancer tissue is done by a machine learning algorithm to separate them into two classes. The proposed method is based on a support-vector-machine-based classifier by dissociating 10 features extracted from the A-line, texture, and phase map by the swept-source optical coherence tomographic intensity and phase images. A set of 88 freshly excised breast tissue [44 normal and 44 cancers (invasive ductal carcinoma tissues)] samples from 22 patients was used in our study. The algorithm successfully classifies the cancerous tissue with sensitivity, specificity, and accuracy of 91.56%, 93.86%, and 92.71% respectively. The present computational technique is fast, simple, and sensitive, and extracts features from the whole volume of the tissue, which does not require any special tissue preparation nor an expert to analyze the breast cancer as required in histopathology. Diagnosis of breast cancer by extracting quantitative features from optical coherence tomographic images could be a potentially powerful method for cancer detection and would be a valuable tool for a fine-needle-guided biopsy.

Multi-spectral quantitative phase imaging (QPI) is an emerging imaging modality for wavelength dependent studies of several biological and industrial specimens. Simultaneous multi-spectral QPI is generally performed with color CCD cameras. Here, we present a new approach for accurately measuring the color crosstalk of 2D area detectors, without needing prior information about camera specifications. Color crosstalk is systematically studied and compared using compact interference microscopy on two different cameras commonly used in QPI, single chip CCD (1-CCD) and three chip CCD (3-CCD). The influence of color crosstalk on the fringe width and the visibility of the monochromatic constituents corresponding to three color channels of white light interferogram are studied both through simulations and experiments. It is observed that presence of color crosstalk changes the fringe width and visibility over the imaging field of view. This leads to an unwanted non-uniform background error in the multi-spectral phase imaging of the specimens. The color crosstalk of the detector is observed to be the limiting factor for phase measurement accuracy of simultaneous multi-spectral QPI systems.

Quantitative phase imaging (QPI) of biological cells and tissues is an important technique useful in the determination of many biophysical parameters such as morphology, refractive index, thickness, cell dry mass, hemoglobin concentration, etc. Off-axis digital holography has been ideal for the QPI of microscopic specimens, but it has lower temporal stability compared to on-axis and common path digital holographic microscopes, which offer higher temporal stability. In this paper, we present a very simple, easy to align yet highly stable common path digital holographic microscope based on a Fresnel biprism interferometer. The system uses a biprism to divide the incoming beam into reference and object beams without the loss of optical power, unlike diffraction phase microscopy. Two methods are proposed, one by utilizing the spatial filtering mode and the other by the self-referencing mode. It offers the advantage that the reference beam can be easily created simply by translating the object in the focal plane of the microscopic objective or by spatially filtering one of the object beams in the Fourier domain. The proposed setup offers no power loss and a high phase stability of approximately 0.006 rad (6 mrad) without using any vibration isolation. The experiments on industrial and biological samples are reported demonstrating its application both for static and dynamic samples.