Phase contrast microscope is an extremely useful device in teaching and research labs. It is a two step process: (1) separation of deviated and undeviated components in the light transmitted through the specimen with a p/2 phase difference between them and (2) obtaining an additional p/2 phase separation thereby converting phase information into amplitude (intensity) contrast for display. Recently we demonstrated the principle of a novel user-friendly Fourier phase contrast microscopy (FPCM) technique with potential for enhanced performance exploiting monochromaticity and phase coherence characteristics of a low power laser and photo-thermal induced birefringence of nematic liquid crystal. As the deviation angle depends on the line width of the source, laser facilitates well resolved spatial frequency (object information) mapping in the Fourier plane. High degree of phase coherence preserves the phase retardation. When the liquid crystal cell is placed at the Fourier plane, low spatial frequencies at the center are intense enough (achieved by the fine control of the source intensity) to induce local liquid crystal molecules into isotropic phase whereas high spatial frequencies on the edges are not so intense and remain in the anisotropic liquid crystal phase resulting in p/2 phase difference between high and low spatial frequencies. Thus it acts as an all-optical self-adaptive variable phase filter and no voltage is required across the cell to align the molecules. Preliminary results on live biological specimens show good image contrast (resulting in display of additional features as well as a more clear display of same features) compared to the images obtained with commercial microscopes. Since the condenser annulus - phase plate combination (used in commercial phase contrast microscope) is not required in our system, the images are free from artifacts. In this R21 application, we will develop all-optical self-adaptive FPCM by optimizing various parameters involved in the design, quantitatively asses the performance of the system in comparison to commercial instrumentation and develop a new and improved Fourier phase contrast microscopy technique for biomedical research. This system is capable of performing a variety of functions: (1) imaging phase objects at micrometer resolution with improved image contrast, (2) imaging phase objects embedded in a scattering medium, and (3) discriminating amplitude and phase objects by incorporating a polarizer before the detector. A multidisciplinary team of researchers with expertise in physics and biology has been assembled to ensure thorough investigation. Our main goal is to develop a rugged, reliable and versatile system, readily available not only for research but also teaching in biological and biomedical labs. When full potential of the technique is demonstrated, we believe that this innovative technology offers several advantages over current state of the art instrumentation and may result in significant breakthroughs in biomedical research.
We propose to optimize various parameters involved in the design, quantitatively assess the performance of the system and develop Fourier phase contrast microscopy technique for biomedical research. The novelty of the system lies in exploiting the advantages offered by a coherent source, optical Fourier transformation and photo-thermal induced birefringence property of a liquid crystal.
| Das, Bhargab; Yelleswarapu, Chandra S; Rao, Dvgln (2012) Parallel-quadrature phase-shifting digital holographic microscopy using polarization beam splitter. Opt Commun 285:4954-5960 |
| Das, Bhargab; Yelleswarapu, Chandra S; Rao, D V G L N (2012) Quantitative phase microscopy using dual-plane in-line digital holography. Appl Opt 51:1387-95 |
| Das, Bhargab; Yelleswarapu, Chandra S; Rao, D V G L N (2012) Dual-channel in-line digital holographic double random phase encryption. Opt Commun 285:4262-4267 |
| Das, Bhargab; Yelleswarapu, Chandra S (2010) Dual plane in-line digital holographic microscopy. Opt Lett 35:3426-8 |
