Dalip Singh Mehta

Enhanced photoluminescence in gold nanoparticles doped ferroelectric liquid crystals

We report the characterization and photoluminescence (PL) of newly synthesized deformed helix ferroelectric liquid crystal (DHFLC) material having short pitch and high spontaneous polarization. We observed ninefold enhancement in PL intensity in gold nanoparticles doped DHFLC material. This enhancement in the PL intensity has been attributed to the coupling of localized surface plasmon resonance from metal nanoparticles with DHFLC molecules, resulting in the increase in excitation and emission rate of the liquid crystal molecules in the localized electromagnetic field. These studies would provide a cutting edge tool in the realization of enhanced photoluminescent liquid crystal display devices.

Nonvolatile memory effect based on gold nanoparticles doped ferroelectric liquid crystal

Nonvolatile memory effect based on gold nanoparticles (GNPs) doped deformed helix ferroelectric liquid crystal (DHFLC) has been observed. This observed memory effect has been attributed to electric field induced charge transfer from liquid crystal molecules to the GNPs and the stabilization of helix deformation of DHFLC material, which occurs on the application of electric field beyond a critical field. The memory effect has been analyzed by polarizing optical microscopy, high-resolution transmission electron microscopy, and dielectric spectroscopy. The observed memory effect combines two active research areas: nanotechnology and liquid crystal.

Fingerprint detection using full-field swept-source optical coherence tomography

We report the application of full-field swept-source optical coherence tomography for fingerprint detection. This system consists of a superluminescent diode as broadband light source and an acousto-optic tunable filter as wavelength-tuning device. The conventional optical coherence tomographic system was modified by coating aluminum oxide on one side of the beam splitter which is used as reference mirror and fingerprints on the glass slide as object. Low-coherence interferometry, nonmechanical scanning, and compactness are the main advantages of the proposed system over conventional fingerprint detection techniques. The present technique is noninvasive in nature and does not require any physical or chemical processing.

Simultaneous topography and tomography of latent fingerprints using full-field swept-source optical coherence tomography

We demonstrate simultaneous topography and tomography of latent fingerprints using full-field swept-source optical coherence tomography (OCT). The swept-source OCT system comprises a superluminescent diode (SLD) as broad-band light source, an acousto-optic tunable filter (AOTF) as frequency tuning device, and a compact, nearly common-path interferometer. Both the amplitude and the phase map of the interference fringe signal are reconstructed. Optical sectioning of the latent fingerprint sample is obtained by selective Fourier filtering and the topography is retrieved from the phase map. Interferometry, selective filtering, low coherence and hence better resolution are some of the advantages of the proposed system over the conventional fingerprint detection techniques. The present technique is non-invasive in nature and does not require any physical or chemical processing. Therefore, the quality of the sample does not alter and hence the same fingerprint can be used for other types of forensic test. Exploitation of low-coherence interferometry for fingerprint detection itself provides an edge over other existing techniques as fingerprints can even be lifted from low-reflecting surfaces. The proposed system is very economical and compact.

Quantitative phase imaging of human red blood cells using phase-shifting white light interference microscopy with colour fringe analysis

We report quantitative phase imaging of human red blood cells (RBCs) using phase-shifting interference microscopy. Five phase-shifted white light interferograms are recorded using colour charge coupled device camera. White light interferograms were decomposed into red, green, and blue colour components. The phase-shifted interferograms of each colour were then processed by phase-shifting analysis and phase maps for red, green, and blue colours were reconstructed. Wavelength dependent refractive index profiles of RBCs were computed from the single set of white light interferogram. The present technique has great potential for non-invasive determination of refractive index variation and morphological features of cells and tissues.

Intensity Distribution Across a Source from Spectral Measurements

Abstract The degree of spectral coherence (μ12(ω)) over the plane of a double slit is determined from the measurement of spectral changes in Youngs interference experiment using the spectral interference law. The experimental and theoretically calculated values of μ12(ω)) for the experimental parameters agree well within experimental error, thus supporting the theoretical prediction of D. F. V. James and E. Wolf (1991, Phys. Lett. A, 157 6). The degree of spectral coherence determined is used for estimating the intensity distribution across a source. This new approach, being a simple spectral measurement technique, might find its application in astronomy, particularly for the study of intensity distribution across stars.

Laser speckle reduction by multimode optical fiber bundle with combined temporal, spatial, and angular diversity.

We report significant speckle reduction in a laser illumination system using a vibrating multimode optical fiber bundle. The optical fiber bundle was illuminated by two independent lasers simultaneously. The beams from both lasers were first expanded and collimated and were further divided into multiple beams to illuminate the fiber optic bundle with normal and oblique incidence. Static diffusers were also placed at the input and output faces of the fiber bundle, thus introducing the spatial as well as angular diversity of illumination. Experiments were carried out both in free space and in imaging geometry configuration. Standard deviation, speckle contrast and signal-to-noise ratio of the images were computed, and the results were compared with those of white light illumination. Speckle contrast close to that of white light was obtained using a vibrating fiber bundle with combined temporal, spatial, and angular diversities of the illumination.

Spectral changes due to source correlation in Young's interference experiment

Abstract In this communication we show that spectral changes are produced on superposing partially coherent light emerging from two pinholes in Youngs interference experiment. These changes have been studied for on-axis and off-axis points of observation.

Simple multifrequency and phase-shifting fringe-projection system based on two-wavelength lateral shearing interferometry for three-dimensional profilometry

We propose a simple multifrequency spatial-carrier and phase-shifting fringe-projection system based on two-wavelength lateral shearing interferometry (LSI). In this system a wedge-shaped plate lateral shearing interferometer is used and, owing to the presence of tilt, a finite number of fringes parallel to the direction of the shear appears; hence a significant spatial-carrier frequency is generated at the focus position. We further enhance the spatial-carrier frequency either by changing the wavelength of the laser light or by slight defocusing. A synthetic interferogram with low spatial-carrier frequency is obtained by use of laser light of two wavelengths simultaneously in the lateral shear interferometer. We obtain the phase-shifted fringe patterns from the same setup by simply moving the wedge plate in an in-plane parallel direction, using a linear translator. The fringe projection system was tested for measurement of the three-dimensional shape of a discontinuous object. The present system has many advantages; e.g., it is a common-path interferometry and hence is insensitive to external vibrations, is compact in size, and is relatively inexpensive.

Enhancement of light extraction efficiency of organic light emitting diodes using nanostructured indium tin oxide

Improved outcoupling efficiency of organic light emitting diodes (OLEDs) is demonstrated by incorporating a nanostructured indium tin oxide (NSITO) film between a conducting anode and a glass substrate. NSITO film was fabricated using rf-sputtering at oblique angle (85°). Significant reduction in refractive index and improved transmission of NSITO film was observed. OLEDs were then fabricated onto NSITO film to extract the ITO-glass waveguided modes. Extraction efficiency was enhanced by 80% without introducing any detrimental effects to operating voltage, current density, and angular invariance of emission spectra of OLEDs.