Vishesh Dubey

Quantitative phase imaging of biological cells using spatially low and temporally high coherent light source.

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.

Ultra-short longitudinal spatial coherence length of laser light with the combined effect of spatial, angular, and temporal diversity

We demonstrate ultra-high axial-resolution topography and tomography of multilayered objects using pseudo thermal light source, i.e., laser. The longitudinal spatial coherence (LSC) length of light was significantly reduced by synthesizing a pseudo thermal source with the combined effect of spatial, angular, and temporal diversity. Thus, generating a low spatially coherent (i.e., broad angular frequency spectrum) light source having narrow temporal frequency spectrum. The LSC length was reduced less than 10 μm using a very low magnification lens. Experimental results of optical sectioning of multilayer objects with high axial-resolution of the order of 4 μm was achieved which is comparable to broadband light source. The present system does not require any dispersion compensation optical system for biological samples as a highly monochromatic light source is used.

Multispectral quantitative phase imaging of human red blood cells using inexpensive narrowband multicolor LEDs

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.

Polarization interferometric digital holographic microscope for quantitative phase imaging and coherent noise reduction

In digital holographic interferometry (DHI), coherent noise degrades accuracy of phase information. We present multi-beam polarization DHI in which two cross polarized interferograms are recorded. Fourier analysis of interferograms reduces coherent noise and increases accuracy.

Quantitative phase imaging using spectrally resolved white light interferometry

A spectrally resolved white light interferometry is demonstrated using a discrete spectrum light sources (i.e., RGB LEDs) and monochrome CCD camera for the multi-color quantitative phase imaging of biological cells without color cross talk.

White light phase shifting interferometry and color fringe analysis for the detection of contaminants in water

We report white light phase shifting interferometry in conjunction with color fringe analysis for the detection of contaminants in water such as Escherichia coli (E.coli), Campylobacter coli and Bacillus cereus. The experimental setup is based on a common path interferometer using Mirau interferometric objective lens. White light interferograms are recorded using a 3-chip color CCD camera based on prism technology. The 3-chip color camera have lesser color cross talk and better spatial resolution in comparison to single chip CCD camera. A piezo-electric transducer (PZT) phase shifter is fixed with the Mirau objective and they are attached with a conventional microscope. Five phase shifted white light interferograms are recorded by the 3-chip color CCD camera and each phase shifted interferogram is decomposed into the red, green and blue constituent colors, thus making three sets of five phase shifted intererograms for three different colors from a single set of white light interferogram. This makes the system less time consuming and have lesser effect due to surrounding environment. Initially 3D phase maps of the bacteria are reconstructed for red, green and blue wavelengths from these interferograms using MATLAB, from these phase maps we determines the refractive index (RI) of the bacteria. Experimental results of 3D shape measurement and RI at multiple wavelengths will be presented. These results might find applications for detection of contaminants in water without using any chemical processing and fluorescent dyes.

High-resolution white light interferometry for quantitative phase imaging of human red blood cells using three-chip colour camera

Quantitative phase imaging of unstained healthy and unhealthy (typhoid) red blood cells at different wavelengths. Digital imaging processing was applied to extract the phase information for red and green wavelength from single white light interferogram.

Longitudinal spatial coherence gated high-resolution tomography and quantitative phase microscopy of biological cells and tissues with uniform illumination

We report longitudinal spatial coherence (LSC) gated high-resolution tomography and quantitative phase microscopy of biological cells and tissues with uniform illumination using laser as a light source. To accomplish this a pseudo thermal light source was synthesized by passing laser beams through an optical system, which is basically a speckle reduction system with combined effect of spatial, temporal, angular and polarisation diversity. The longitudinal spatial coherence length of such light was significantly reduced by synthesizing a pseudo thermal source with the combined effect of spatial, angular and temporal diversity. This results in a low spatially coherent (i.e., broad angular frequency spectrum) light source with narrow temporal frequency spectrum. Light from such a pseudo thermal light source was passed through an interference microscope with varying magnification, such as, 10X and 50X. The interference microscope was used for full-field OCT imaging of multilayer objects and topography of industrial objects. Experimental results of optical sectioning of multilayer biological objects with high axial-resolution less than 10μm was achieved which is comparable to broadband white light source. The synthesized light source with reduced speckles having uniform illumination on the sample, which can be very useful for fluorescence microscopy as well as quantitative phase microscopy with less phase noise. The present system does not require any dispersion compensation optical system for biological samples as a highly monochromatic light source is used.

Quantitative phase imaging using white light interference microscopy with color fringe analysis: A comparative study of color interferograms recorded by single chip and 3-chip CCD color camera

We demonstrate results for phase maps of biological cells using white-light and multi-spectral interference microscopy. Study on comparison of phase maps reconstructed using 1-CCD and 3- CCD is presented to reduce color cross-talk and improved resolution.

Fiber-Optic Micro-Endoscopy for Imaging Biological Cells at Remote Location and Depixelation of Images Using Discrete Cosine Transform

Ahstract- High resolution wide field fluorescent imaging is demonstrated using imaging fiber bundle which contain 30000 numbers of single mode fibers. Further discrete cosine transform method applied to eliminate pixilation of image without sacrificing the resolution.