Diffraction properties of highly birefringent liquid-crystal composite gratings.

We have fabricated electrically switchable holographic gratings, using Polaroid Corporation's 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.

Electro-optic modulation in an anisotropic artificial Kerr medium.

We describe the performance of intensity and phase modulators that use an aqueous suspension of polytetrafluoroethylene (PTFE) microparticles. In this medium, the electro-optic effect is caused by the reorientation of anisotropic microparticles in an applied electric field. The intensity modulator was constructed in the Kerr geometry by the use of a sample path length of 20 µm. The response time of the modulator is less than 25 ms, and the depth of modulation was measured to be 28 dB for a switching voltage of 134 V(rms). The switching voltage necessary to achieve a π-phase shift with the phase modulator is less than 30 (Vrms).

Optically switched volume holographic elements.

We optically switched the diffraction efficiency of volume holographic elements recorded in DMP-128 photopolymer by use of a thermal nonlinearity of the liquid crystal 5CB. The liquid crystal was incorporated into the volume grating. The diffraction efficiency of small areas of the grating was switched with a control beam power of several milliwatts. The intensity of a signal beam at a different wavelength and arbitrary power was switched with time constants below 1 ms.

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.

Simultaneous wave-front and polarization conjugation of picosecond optical pulses by stimulated Rayleigh-wing scattering.

Using phase conjugation by stimulated Rayleigh-wing scattering (SRWS) in carbon disulfide, we have observed simultaneous correction of wave-front and polarization distortions. SRWS was excited by pulses of 20-psec duration containing as much as 15 microJ of energy at a wavelength of 0.53 microm and produced phase-conjugate reflectivities as large as 10%.

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.

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 ultrasound's efficacy on the medium's temperature during insonation and a significant reduction of ultrasound efficacy in compromising cellular integrity in the presence of cysteamine.

An explanation for the decrease in cell lysis in a rotating tube with increasing ultrasound intensity.

Previous observations indicate that for in vitro mammalian cells insonated in rotating test tube the amount of cell lysis initially increases to some maximum and then decreases with further increase in ultrasound exposure. The results of the present investigation support the postulate that the reduction in cell lysis with increase in ultrasound intensity is related to the development of an ultrasonically induced "cloud" of bubbles in the fluid between the transducer and test tube; these bubbles mitigate against acoustic transmission thus reducing cell lysis in the insonated test tube.