Volume 98, Issue 10, 15 November 2005
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
98(2005); http://dx.doi.org/10.1063/1.2132511View Description Hide Description
Moderate air-hole-fraction photonic crystal square lattice structures defining small cavity resonators were created by etching air holes of radius to a depth of in an all-polymer slab waveguide. Transmission measurements with subnanometer resolution resolved the complete transmission spectra and highly resonant defect peaks with quality factors larger than 400. Simulations demonstrate the importance of high-aspect-ratio etching depths for maintaining vertical index-confinement and vertically quasisymmetric field distributions despite the material index asymmetry. Experimental spectra are shown to match the three-dimensional finite-integration simulations. Enhanced quality factors of up to were found in the simulations for cavities bounded by modified radius air holes. In this manner resonators with very low out-of-cavity losses and high defect state transmission may be created in moderate index contrast polymer waveguide slabs.
98(2005); http://dx.doi.org/10.1063/1.2134880View Description Hide Description
We recently reported on the realization of ultraviolet photonic crystal laser based on zinc oxide [Appl. Phys. Lett.85, 3657 (2004)]. Here we present the details of structural design and its optimization. We develop a computational supercell technique that allows a straightforward calculation of the photonicband structure of ZnOphotonic crystal slab on sapphire substrate. We find that despite the small index contrast between the substrate and the photonic layer, the low-order eigenmodes have predominantly transverse-electric (TE) or transverse-magnetic polarization. Because emission from ZnO thin film shows a strong TE preference, we are able to limit our consideration to TE bands, spectrum of which can possess a complete photonic band gap with an appropriate choice of structure parameters. We demonstrate that the geometry of the system may be optimized so that a sizable band gap is achieved.
98(2005); http://dx.doi.org/10.1063/1.2135411View Description Hide Description
The room-temperature Raman spectra of single crystals of GaSe, GaS, and mixed compounds with were measured with a HeNe laser in confocal configuration. The changes in the spectra indicate changes of the crystal structure. The spectra of pure GaSe and of the mixed compound with show pronounced photoluminescence signals blueshifted from the laser line, whereas these signals do not appear for higher sulfur content. Their origin is interpreted as second-harmonic generation in the laser focus causing the formation and radiative decay of Wannier excitons.Two-photon absorption is ruled out, since the effect is absent in the centrosymmetric crystals with . With a green laser whose photon energy is larger than the band gap, strong photoluminescence is also observed in crystals with higher sulfur content.
98(2005); http://dx.doi.org/10.1063/1.2136426View Description Hide Description
The improvement of the laser performances of an unprocessed cleavage microchip has been reported. Pumped by a Ti:sapphire laser at , quasi-cw output laser power up to around wavelength with slope efficiency near 52% has been obtained in an end-pumped plano-plano resonator. The influence of the ratio between the cavity mode and pump beam area on the laser performances and laser spectra at various output powers has been investigated. The experimental results have shown that the cleavage technique can become a practical and effective method to obtain the microchip laser medium easily and directly.
98(2005); http://dx.doi.org/10.1063/1.2133903View Description Hide Description
Solid deuterium-tritium (D-T) fuel layers inside copper-doped beryllium shells are robust inertial confinement fusion fuel pellets. This paper describes the first characterization of such layers using phase-contrast x-ray imaging. Good agreement is found between calculation and experimental contrast at the layer interfaces. Uniform solid D-T layers and their response to thermal asymmetries were measured in the Be(Cu) shell. The solid D-T redistribution time constant was measured to be 28 min in the Be(Cu) shell.