Thin Holographic Gratings Research Articles

Off-axis digital holographic camera for quantitative phase microscopy.

We propose and experimentally demonstrate a digital holographic camera which can be attached to the camera port of a conventional microscope for obtaining digital holograms in a self-reference configuration, under short coherence illumination and in a single shot. A thick holographic grating filters the beam containing the sample information in two dimensions through diffraction. The filtered beam creates the reference arm of the interferometer. The spatial filtering method, based on the high angular selectivity of the thick grating, reduces the alignment sensitivity to angular displacements compared with pinhole based Fourier filtering. The addition of a thin holographic grating alters the coherence plane tilt introduced by the thick grating so as to create high-visibility interference over the entire field of view. The acquired full-field off-axis holograms are processed to retrieve the amplitude and phase information of the sample. The system produces phase images of cheek cells qualitatively similar to phase images extracted with a standard commercial DHM.

PHOTOREFRACTIVE AND PHOTOCONDUCTIVE FEATURES OF THE NANOSTRUCTURED MATERIALS

Photoconductive and photorefractive characteristics of fullerene- and nanotubes-doped organic thin films based on conjugated organics, such as polyimide, polyaniline, pyridine, etc. have been studied. In addition, the liquid crystal mesophase with nanoobjects has been investigated. The increase of the charge carrier mobility of nanosensitized organics has been established. The nonlinear refraction and cubic nonlinearity have been investigated at wavelength of 532 nm via four-wave mixing technique using Raman-Nath diffraction regime. The thin holographic grating has been written at the spatial frequencies placed in the range of 90-150 mm-1. The energy density has been chosen in the range of 0.1-0.9 J × cm-2. The correlation between photoconductive and nonlinear optical parameters has been revealed. The nanostructured materials can be proposed for different area of nano- and microelectronic applications.

Optical investigations of a C70-doped 2-cyclooctylamino-5-nitropyridine liquid crystal system

Thin holographic gratings in a C70-doped 2-cyclooctylamino-5-nitropyridine–liquid crystal system have been investigated under nano- and picosecond pulsed laser irradiation at a wavelength of 532 nm. From the results obtained, the nonlinear refractive index n2 and third-order susceptibility χ(3) have been determined. The potential use of the system studied in the modulation and generation of laser irradiation over the visible spectral range has been evaluated. The rotational ability of fullerene to strengthen the alignment of the LC molecule director has been discussed.

Holographic recording in thin C 70-doped polymer organic films

The dynamic and static thin holographic gratings have been recorded in C 70-doped photosensitive polyimide 6B and 2-cyclooctylamino-5-nitropyridine. The drastic change in diffraction efficiency has been observed under the Raman–Nath diffraction condition using the second harmonic of pulse Nd laser. The threshold of the transition from phase grating to amplitude one has been determined. The results obtained have been explained by the absorption spectral peculiarities of the fullerene-doped films and by their thermal properties.

Grating oscillations in photorefractive crystals

A theoretical analysis is presented that describes wave-mixing processes in thin holographic gratings for phase-modulated beams. Experiments with photorefractive Bi(12)TiO(20) crystals in which the signals for Bragg diffraction and for the first non-Bragg diffraction order were measured support the analysis.

Hybrid resonant/near-resonant photorefractive structure: InGaAs/GaAs multiple quantum wells

A photorefractive structure was grown which was composed of shallow In0.1Ga0.9As/GaAs quantum wells on a photorefractive GaAs substrate. The quantum-well exciton energy is adjusted with In content to coincide with the optimum photon energy for near-resonant photorefractive effects in the substrate. The photorefractive quantum wells also operate as thin holographic gratings in four-wave mixing without the removal of the substrate, simplifying the fabrication of photorefractive quantum-well devices.