Volume 95, Issue 11, 01 June 2004
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
95(2004); http://dx.doi.org/10.1063/1.1710722View Description Hide Description
The alignment of nematic liquid crystals in a hybrid cell can be easily reconfigured by applying an external electric field. We exploit this feature to realize a waveguidingstructure whose refractive index profile can be dynamically reshaped. The mode structure of the guided light, investigated by m-lines spectroscopy at various electric field strenghts, can be well predicted by a parameter-free model based on the elastic,dielectric, and optical properties of the liquid crystal. According to such a model, the field profiles of the modes supported by hybrid nematic waveguides display very peculiar features.
95(2004); http://dx.doi.org/10.1063/1.1710721View Description Hide Description
Focusing a transversely excited atmospheric laser beam in air atmospheres induced a blast wave. The kinetic energy of a laser-induced blast wave was determined from shadowgraph images of shock wave expansion. Results showed that the fraction of input laser energy that is converted into the blast wave energy decreased from 0.45 to 0.2 concomitant with the decrease in ambient pressure from 100 to 10 kPa. Also, it was insensitive to input laser energy from 4 to 13 J.
95(2004); http://dx.doi.org/10.1063/1.1713045View Description Hide Description
Terahertz (THz)-wave generation using difference-frequency mixing in an organic 4-N, N-dimethylamino--methyl-stilbazolium tosylate (DAST) crystal was investigated theoretically and experimentally. We developed a dual-wavelength optical parametric oscillator(OPO) with two crystals as the input light source. This oscillator has a tunable range from 1300–1450 nm and is pumped by a diode-pumped, frequency-doubled, Q-switched Nd:YAG laser with a pulse duration of 10 ns. Widely tunable THz waves ranging from 2 to 20 THz were generated from DAST crystals with 0.5- and 1-mm thickness using the OPO. THz output energies of 82 nJ (peak power of 10.3 W) at 11.6 THz and 110 nJ (peak power of 13.8 W) at 19 THz were obtained with a 1-mm-thick DAST crystal. Using a tunable THz-wave system consisting of the THz source and a pyroelectricdetector, THz spectroscopic data for a polytetrafluoroethylene sheet were obtained and were comparable to data obtained from a conventional far-infrared spectrometer.
95(2004); http://dx.doi.org/10.1063/1.1713028View Description Hide Description
We analyze the ability of the Bragg reflectormodel to account for the properties of metallo-dielectric photonic crystals. We perform mm-wave transmission measurements on photonic structure consisting of conducting spheres in air and compare our results to the model predictions. In particular, we verify the universal relation between the Bragg attenuation length and the width of the photonic stopband, which is predicted by the Bragg reflectormodel.