Michelle S. Malcuit

Diffraction properties of highly birefringent liquid-crystal composite gratings

We have fabricated electrically switchable holographic gratings, using Polaroid Corporations DMP-128 photopolymer filled with the nematic liquid crystal E7. It is shown that a coupled-wave theory that includes the effects of the birefringence of the liquid crystal must be used to explain the diffraction properties of these anisotropic volume gratings. Furthermore, a detailed comparison of theory and experiment provides information about the alignment of the liquid crystal within the polymer host.

Two-photon conical emission

Abstract A two-photon resonantly enhanced four-wave mixing (FWM) process leading to the conical emission of two new frequency components has been observed in atomic sodium vapor. A dye laser tuned close to the 3s → 3d two-photon allowed transition produces broad-band emission near the frequencies of the 3d → 3p and 3p → 3s transitions. This radiation is emitted in the forward direction in the form of cones surrounding the transmitted laser beam. The dependence of the cone angle on the emission wavelength and atomic number density is in excellent agreement with the predictions of a model that ascribes the origin of the conical emission to a phase-matched four-wave mixing process.

Optical bistability in nonlinear periodic structures

Optical switching and optical bistability and multistability are observed experimentally with a nonlinear periodic structure. The periodic dielectric is a colloidal crystal that exhibits a large electrostrictive nonlinearity. The transmission characteristics of these crystals as a function of incident intensity are presented for several different frequencies of light within the stopgap of the periodic structures.

Optical power limiting with nonlinear periodic structures

We present observations of optical power limiting using a thermal nonlinearity in a dye-doped colloidal crystal. The transmission of the crystal is studied as a function of the incident intensity for various dye concentrations, lattice spacings, and wavelengths. We have found that optical limiting occurs when the wavelength of the incident light is tuned to the blue edge of the stop gap of these structures. Limiting intensities near 10 kW/cm(2) have been obtained for colloidal solutions with 10(-5) M Kiton Red dye. The experimental results are compared with theoretical models of nonlinear distributive-feedback structures in which the nonlinearity is assumed to be thermal.

Enhancement of the nonlinear optical properties of fluorescin doped boric-acid glass through cooling

We examine, both theoretically and experimentally, the temperature dependence of the nonlinear optical response of fluorescein doped boric-acid glass. The third-order nonlinear susceptibility is increased by an order of magnitude over its room temperature value to greater than 10 esu by cooling the sample to a temperature below 200 K.

Transmission properties of refractive index-shifted Bragg gratings

Abstract We present an analysis of the transmission properties of index-shifted Bragg gratings. Theoretical predictions of the transmission properties of these gratings are obtained using a generalized transfer matrix method. Our theoretical predictions show that a precise modification of the average refractive index of Bragg gratings can lead to the generation of narrowband transmission windows within a broad low transmission band. The theoretical predictions are compared to experimental results obtained with fiber Bragg gratings.

Polarization-sensitive holograms formed using DMP-128 photopolymer

Abstract The diffraction efficiency of volume holographic gratings can depend strongly on the state of polarization of the incident light. We have experimentally studied the diffraction properties of highly polarization-sensitive, volume holographic gratings in the highly modulated regime formed using DMP-128 photopolymer and have compared data in this regime to existing theories. We have found that rigorous coupled-wave theory accurately predicts experimental measurements of the diffraction efficiency in the highly-modulated, polarization-sensitive regime, while a simpler two-wave theory modified to include form birefringence does not.

Vector phase conjugation by two-photon-resonant degenerate four-wave mixing

We have studied the polarization properties of phase conjugation by degenerate four-wave mixing resonantly enhanced by the sodium 3S1/2 → 6S1/2 two-photon-allowed transition. As predicted by third-order theories, this interaction leads to simultaneous conjugation of the optical wave front and state of polarization (vector phase conjugation) when the pump intensities are sufficiently weak. However, qualitatively different polarization behavior is observed for pump intensities near or above the two-photon saturation intensity.

Confirmation of the protective effect of cysteamine in in vitro ultrasound exposures

Armour and Corry (Radiat. Res. (1982) 89 369-380) reported that ultrasound-induced damage to in vitro Chinese hamster ovary cells was significantly reduced in the presence of cysteamine. The objective of this study was to attempt verification of this result. Four series of experiments were undertaken using in vitro cell suspensions, namely: (1) determination of the effect of cysteamine concentration on cell growth; (2) determination of the temperature dependence of ultrasonically induced cell damage; (3) determination of a dose-response relationship for the cytotoxicity of cysteamine; and (4) assessment of cell integrity and reproductive capacity in the presence or absence of cysteamine during ultrasonic exposure. Ultrasound parameters included a resonance frequency of 1 MHz, a continuous wave exposure duration of 5 min, and intensities from 0 to 21.6 W cm-2. The results indicated a dependence of ultrasounds efficacy on the mediums temperature during insonation and a significant reduction of ultrasound efficacy in compromising cellular integrity in the presence of cysteamine.

Switched grating devices for phased-array applications

Free space optical systems are described that use switchable grating technology and nonlinear materials to form digital time shifters. A cascade of n independently controlled gratings provides 2n evenly spaced time delay paths. Featured characteristics including potential for excellent switch isolation, spurious beam and crosstalk suppression, reduction in complexity, and low insertion loss are discussed in the context of phased array applications. Varied configurations are discussed including hybrid free- space/guided wave configurations for long time delays; transmission and double-pass digital optical time shifters; and entire array drivers that replace many single-channel time shifters with a single configuration. Using free space micro-optics, many independent time shifter configurations can be compactly stacked. A novel noise suppression device is discussed that enhances the channel isolation and signal purity of the systems.