Volume 95, Issue 7, 01 April 2004
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Synthesis and spectroscopic characterization of single crystal for highly efficient 1.53 μm amplification95(2004); http://dx.doi.org/10.1063/1.1649807View Description Hide Description
A single crystal was grown by the Tammann–Stober method. The potential of this material as a laser crystal for 1530 nm emission was established by quantitative analysis of the optical absorption and emission spectra. Assuming the tetragonal symmetry of the sites, the crystal field parameters, Racah parameters, spin–orbit interaction parameters, and configuration interaction parameters were derived by fitting the experimental absorption band positions with the model energy Hamiltonian. Judd–Ofelt parametrization was done to compute the radiative decay time and fluorescence branching ratio of various meta stable transitions. Using the measured fluorescence decay time and computed radiative decay time, 100% quantum efficiency is obtained for the 1530 nm band, which is reasonable due to the low multiphonon relaxation, and absence of nonradiative energy transfer processes at the 0.01 at.% concentration. The narrow bandwidth (13 nm) and high stimulated emission cross section support the suitability of for use in high gain optical amplifiers.
95(2004); http://dx.doi.org/10.1063/1.1632018View Description Hide Description
We propose a measurement method to determine the cell parameters which are a cell gap thickness, a twist angle and dispersion for a twisted-nematic liquid crystal cell by the spectral method. This method finds the variation point of transmission with respect to the wavelength λ. The proposed method can be applied to the determination of cell thickness and twist angle in the low cell gap as well as to the high cell gap.
95(2004); http://dx.doi.org/10.1063/1.1649808View Description Hide Description
Lanthanide series ions are considered in the context of acquiring spectroscopic parameters and their application to modelling of quasifour-level lasers. Tm:Ho codoped crystals of (YLF) and the isomorphs (LuLF) and (GdLF) as 2.0 μm lasers are used for illustration of the experimental and theoretical techniques presented here. While these materials have similar physical properties, they differ in the strength of the crystal field at the site of optically active lanthanidedopant ions such as and This is due in part to the size of the and ions, which comprise part of the host lattice, but ionicity plays a role as well. This selection of lanthanide: host materials provides a useful basis on which to assess laser materials with regards to changes in the strength of the crystal field at the dopant ion site. It is demonstrated that Tm:Ho:LuLF has a larger crystal field splitting than Tm:Ho:YLF and Tm:Ho:GdLF, leading to smaller thermal populations in the Ho lower laser level. To assess this effect quantitatively, the energy levels of the first ten manifolds in Ho:LuLF have been determined. Measurement of (X=Y,Lu,Gd) emission cross sections at 2.0 μm, pump absorption cross sections around 0.78 μm, manifold to manifold decay times and energy transfer parameters in systems are also determined to provide a consistent set of parameters to use in laser modeling. The techniques presented here are applicable to any lanthanide series ion in a crystalline host. A theoretical laser model has been developed that is easily adapted to any lanthanide ion in a crystal host. The model is used to predict diode side-pumped laser performance of Tm:Ho:LuLF and Tm:Ho:YLF using input parameters determined from the spectroscopy presented here. An explanation is presented for the improved performance of Tm:Ho:LuLF over Tm:Ho:YLF by modeling the laser. A demonstration that small changes in lower laser thermal population can substantially alter laser performance is noted, an effect that has not been fully appreciated previously.
95(2004); http://dx.doi.org/10.1063/1.1650895View Description Hide Description
An optoelectronic analog feedback circuit uses dynamic holography to perform independent component analysis on an array of input signals imposed on a set of optical carriers. The requisite nonlinearity for achieving high-order statistical analysis is established with optical phase modulation in the feedback loop. The dynamics of the system is shown to be driven by the statistical characteristic functions of the input signals and reveals winner-takes-all dynamics when at least one of the signals is sub-Gaussian. Signal correlation and circuit adaptation is carried out by the dynamic holographic medium and therefore takes place in a parallel fashion. The allowed signal bandwidth is limited by the delay time of the feedback loop, thus signal bandwidths exceeding 100 MHz should be possible using relatively standard electronic and optoelectronic technology. Moreover, the scheme can directly accommodate microwave carrier frequencies to several tens of gigahertz.
95(2004); http://dx.doi.org/10.1063/1.1667604View Description Hide Description
Focal length of a laser-induced lens in guest-host liquid crystals (GHLCs) was varied over a wide range by using both large optical nonlinearity and anisotropic complex refractive indices in GHLCs. The characteristics of the laser-induced lens were strongly dependent on the polarization state of the probe beam because the sign of the refractive index change was negative for extraordinary wave, while positive for ordinary one. These characteristics were well explained by theoretical calculating both the optical and thermal properties of the GHLCs.