Volume 96, Issue 6, 15 September 2004
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
96(2004); http://dx.doi.org/10.1063/1.1776315View Description Hide Description
Optically pumped organic polymer lasers are fabricated by spin coating a thin polymer film onto a nanopatterned circular-grating surface-emitting distributed Bragg reflector. For certain grating parameters, we observe a peak inside the stop band that leads to lasing with a reduced threshold. An analytical model, based on the transfer-matrix method, has been developed to investigate the origin of this peak. The theoretical results are in good agreement with the experimental findings.
96(2004); http://dx.doi.org/10.1063/1.1776320View Description Hide Description
A detailed crystal-field splitting analysis is given for the 26 lowest-energy multiplet manifolds,, of in polycrystallineceramicgarnet (YAG). The absorption spectra obtained between and room temperature, and between 1750 and , and the fluorescencespectrum obtained at and observed between 1450 and are analyzed for transitions between individual energy (Stark) levels that characterize the energy-level structure of ions in symmetry sites, replacing ions in the garnet host lattice. A model Hamiltonian including atomic and crystal-field terms is diagonalized within the complete basis set which includes 364 states. The calculated splitting of the energy levels by the crystal field is compared with the experimental splitting observed in both the ceramic sample and a single-crystal laser rod. Both samples have approximately the same concentration, about . By varying the atomic and crystal-field parameters, we obtain a standard deviation of between 106 calculated-to-observed Stark levels found between the ground state and the at . Within this standard deviation the energy-level structure of is found to be similar in both samples. Low temperature visible and near IR spectra of ceramic: show it has comparable properties to the crystalline analog.
96(2004); http://dx.doi.org/10.1063/1.1762709View Description Hide Description
-activated strontiumlanthanum aluminate (ASL:Nd) crystals give efficient laser emission at 900 nm, whose properties depend on the x and y composition parameters. Based on high-resolution spectroscopy and emission decay, this paper demonstrates that the composition dependence of the laser emission is caused by the presence of two structural centers, and whose relative proportion in crystals is determined by composition parameter x. From the spectral data and crystal structure it is inferred that center that prevails at low x, corresponds to a in a site of local symmetry with no nearby or ions. The center lines, prevailing at large x parameter, which are broader and shift with composition, are composite lines of various structural centers of in a site with different occupancy of nearest-neighbor sites by The influence of the spectral and emission dynamics features of these centers on the laser properties is discussed and criteria for the selection of optimal composition is inferred.
96(2004); http://dx.doi.org/10.1063/1.1778219View Description Hide Description
Controlled condensation of water vapor on a nonpolar liquid polymer film leads to the formation of submicrometer arrays of water droplets. Dissolution of a small amount of a polymer surfactant in the volatile liquid prevents the drops from coalescing and stabilizes their hexagonal arrangement. When subsequently the solvent and the water evaporate a solid polymer film patterned with hexagonally ordered holes remains—similar in shape to a honeycomb pattern. The hole size and the polydispersity are controlled by the solvent type, the flow rate of the condensing vapor, and the polymer concentration. The pattern is used as a lithographic mask to structure semiconductor surfaces. To this end, metal is deposited on the prestructured surface and subsequently lifted off to create two complementary structures: an array of metal disks on the semiconductor and a metal network. The lateral periodicity of the patterns can be varied between and several micrometers covering macroscopic areas . Employing the metallic disk pattern as a mask in a plasma dry-etching process we have fabricated two-dimensional photonic crystals with small lattice constants in silicon. We have also used the complementary metal net for the production of metallic dichroic filters. The thin metal net acts as an optical short-pass in the infrared region of the spectrum due to its small lateral structure dimensions. The optical transmission of the dichroic filters is measured and simulated by a model calculation.