Index of content:
Volume 96, Issue 2, 15 July 2004
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Phenomenological model of anisotropic volume hologram formation in liquid-crystal-photopolymer mixtures96(2004); http://dx.doi.org/10.1063/1.1762713View Description Hide Description
The real time formation of anisotropic volume holographic reflection gratings in a liquid-crystal/photopolymer mixture is studied. We develop a phenomenological model of gratingformation that incorporates the photophysics and photochemistry of the initiator dye, reaction-diffusion kinetics of the monomer-polymer system, phase separation of the liquid crystal, nematic order evolution of liquid-crystal droplets, and volume shrinkage of the polymer. We then test this model by experimentally monitoring the diffraction efficiency for s and p polarization, Bragg wavelength, and laser scattering in real time as the grating is formed. The model yields good agreement with experimental data for different recording intensities and exposure times. We discuss the physics of the system as it evolves in time and explain the major features of anisotropicgratingformation in acrylate-based holographicpolymer-dispersed liquid crystals.
96(2004); http://dx.doi.org/10.1063/1.1763225View Description Hide Description
Low frequency fluctuations in light intensity were measured from five different types of commercially available light emitting diodes with wavelengths from 375 nm to 740 nm and from two different halogen lamps. At low frequencies below 10–100 Hz some light emitting diodes(LEDs) can provide lower levels of noise than halogen lamps. A noise quality factor β is proposed in order to characterize noise behavior of LEDs.