Index of content:
Volume 96, Issue 10, 15 November 2004
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Effects of polarizations of a laser on absorption in a paraboloid of revolution-shaped welding or drilling cavity96(2004); http://dx.doi.org/10.1063/1.1797543View Description Hide Description
The effects of polarizations on the apparent absorptivity or integrated energy absorbed by a paraboloid of revolution-shaped cavity subject to a laser beam are systematically and quantitatively investigated. The incident flux is considered to be a mode of a Gaussian distribution specified by the wavelength, spot size, and focal location of the laser beam. Using a Monte Carlo method and neglecting the absorption within the plasma in the cavity, the results show that the predicted energy-transfer efficiency versus incident flux and cavity depth agrees well with the experimental data. The apparent absorption of polarization is found to be always higher than that of polarization, even though the latter causes higher energy fluxes absorbed than the former near the critical radius. The apparent absorptivity for polarization as a function of cavity depth can be divided into three parts: an initial decrease, rapid increase, and gradual increase. Interestingly, the polarization of circularly polarized incoming rays is gradually transformed into polarization in the course of multiple reflections. The apparent absorptivity as a function of polarizations, specular reflectivity, penetration depth, focal location, and absorptive and refractive indices is also presented.
96(2004); http://dx.doi.org/10.1063/1.1805185View Description Hide Description
This work demonstrates the feasibility of using polymer-dispersed liquid crystal(PDLC)films as electrically switchable spatial filters in the optical signal process. The fabrication relies on the fact that the size of the liquid crystaldroplet formed in a PDLCfilm is inversely proportional to the intensity of curing. Controlling the driving voltage on the PDLC sample can filter particular spatial frequencies in the Fourier optical signal process. A simulation is also performed, and the results are highly consistent with those of experiments.
Nonvolatile two-step, two-color holography with continuous-wave lights for both congruent and near-stoichiometric96(2004); http://dx.doi.org/10.1063/1.1794361View Description Hide Description
We have studied theoretically the steady-state nonvolatile two-step, two-color holographic recording performance for both the congruent and the near-stoichiometric based on the two-center model (the deep-trap and the shallow-trap centers are and , respectively). The results show that the direct electron exchange between the centers and the centers due to the tunneling effect dominates the charge-transfer process during the nonvolatile two-step, two-color holography and determines the two-step, two-color holography performance in . We have further studied the effects of the crystal stoichiometry on the performance of the two-step, two-color holography. It is shown that, as far as the total space-charge field is considered, the nonvolatile two-step, two-color holography performance in the near-stoichiometric is much better than that in the congruent within the intensity range reachable by the continuous-wave lights.
96(2004); http://dx.doi.org/10.1063/1.1803946View Description Hide Description
A method for forming periodic reverse-twist domains using a microscale rubbing pattern has been proposed; that is, an isolated twist domain is surrounded by a twist domain. Since liquid crystal(LC) materials exhibit elastic nature, the twist sense of the inner twist domain prefers to be the same as that of the surrounding twist domain. Two factors are investigated to obtain periodic reverse-twist domains; (i) the injection process of LC material (isotropic or nematic phase) and (ii) the ratio of the area of the surrounding twist domain and the whole area (the normalized area of the twist domain). In the case of the injection in isotropic phase, it is revealed that periodic reverse-twist domains can be obtained only when the area of the twist domain is sufficiently large. On the other hand, in the case of injection in nematic phase, periodic reverse-twist domains can successfully obtained regardless of the area of the twist domain. Thus, the injection rocess is a very important factor to obtain periodic reverse-twist domains. The fabricatedLC cell with the periodic reverse-twist domains is applied to LCgrating. The almost linear relationship between the diffraction efficiency and the normalized area of the twist domain is found and the high diffraction efficiency (0.39) near the theoretically maximum value (0.405) is obtained when the normalized area of the twist domain is very small (0.1). The fabricatedLCgrating can function as a polarization-idependent and wavelength-independent LCgrating.