Use of Co2+:MgAl2O4 transparent ceramics in passive Q-switching of an Er:Glass laser at 1.534†µm.

We present the implementation of Co2+:MgAl2O4 transparent ceramics as passive Q-switching elements in an Er:Glass laser at 1.534 µm. Linearly polarized pulsed output was obtained by Brewster angle inclination of the material Q-switching plate relative to the laser axis. Separate pulses were ∼105 ns long (FWHM), exhibiting ∼6.2 kW peak power at near TEM00 quality. Several fundamental sample properties important for laser intracavity operation were measured; thermo-optic coefficient dn/dT = ( - 3.8 ± 1) × 10-5 °C-1, thermal lensing factor L-1d(nL)/dT = 2.59 × 10-5 °C-1, linear expansion coefficient α = (3.9 ± 0.6) × 10-5 °C-1, polarizability thermal coefficient ϕ = (7.2 ± 2.2) × 10-5 °C-1, and damage threshold ∼6.5 J/cm2.

Competing radiative and nonradiative decay of embedded ions states in dielectric crystals: theory, and application to Co2+:AgCl0.5Br0.5.

We present a generally applicable theoretical model describing excited-state decay lifetime analysis of metal ions in a host crystal matrix. In contrast to common practice, we include multi-phonon non-radiative transitions competitively to the radiative one. We have applied our theory to Co2+ ions in a mixed AgCl0.5Br0.5 crystal, and as opposed to a previous analysis, find excellent agreement between theory and experiment over the entire measured temperature range. The fit predicts a zero absolute temperature radiative lifetime τrad(0) = 5.5 ms, more than three times longer than the measured effective low-temperature one τeff(0) = 1.48 ms. Furthermore, the fit configuration potential dissociation energy has been estimated as D = 2500 cm-1 and the lattice vibrational cutoff frequency as hωco = 180 cm-1. We have experimentally verified the latter by optical reflection measurement in the far-IR.

Air-stable PbSe/PbS and PbSe/PbSexS1-x core-shell nanocrystal quantum dots and their applications.

The optical properties and functionality of air-stable PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed shell nanocrystal quantum dots (NQDs) are presented. These NQDs showed chemical robustness over months and years and band-gap tunability in the near infrared spectral regime, with a reliance on the NQD size and composition. Furthermore, these NQDs exhibit high emission quantum efficiencies of up to 65% and an exciton emission band that is narrower than that of the corresponding PbSe NQDs. In addition, the emission bands showed a peculiar energy shift with respect to the relevant absorption band, changing from a Stokes shift to an anti-Stokes shift, with an increase of the NQD diameter. The described core-shell structures and the corresponding PbSe core NQDs were used as passive Q-switches in eye-safe lasers of Er:glass, where they act as saturable absorbers. The absorber saturation investigations revealed a relatively large ground-state cross-section of absorption (sigma gs = 10(-16) - 10(-15) cm2) and a behavior of a "fast" absorber with an effective lifetime of tau eff approximately 4.0 ps is proposed. This lifetime is associated with the formation of multiple excitons at the measured pumping power. The product of sigma gs and tau eff enables sufficient Q-switching performance and tunability in the near infrared spectral regime. The amplified spontaneous emission properties of PbSe NQDs were examined under continuous illumination by a diode laser at room temperature, suitable for standard device conditions. The results revealed a relatively large gain parameter (g = 2.63 - 6.67 cm-1). The conductivity properties of PbSe NQD self-assembled solids, annealed at 200 degrees C, showed an Ohmic behavior at the measured voltages (up to 30 V), which is governed by a variable-range-hopping charge transport mechanism.

Spectroscopy and laser characteristics of copper-vapor-laser pumped pyrromethene-556 and pyrromethene-567 dye solutions.

We measured the basic optical properties of Pyrromethene-567 (P567) and Pyrromethene-556 (P556) dye solutions that are relevant to their application as dye lasers. The fluorescence spectra of methanol solutions show mirror images in relation to the absorption spectra, with Stokes shifts of 29.5 and 37.5 nm, respectively, for the two dyes. The central fluorescence peaks were at 546 and 535 nm, with widths of ~40 and ~50 nm (FWHM). The quantum yields were 97% ? 5% and 78% ? 5% for P567 and P556, respectively. Fluorescence lifetimes of 6.0 ? 0.2 ns were obtained for both dyes in methanol. Laser action, obtained by pumping with the green emission line (510.6 nm) from a copper-vapor laser, was measured in a Hänsch-type cavity. Tunability ranged from 531 to 590 nm for P567 and from 522 to 590 nm for P556. Lasing thresholds were ~0.27 and ~0.16 mJ/pulse, with 25% and 27% slope efficiencies for P567 and P556, respectively. Spectroscopy and lasing were studied in other solvents as well.

Characteristics of 1, 1',3,3,3',3'-hexamethylindotricarbocyanine iodide as a tunable dye laser in the near infrared.

We describe the lasing characteristics of a 1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide infrared dye laser. The absorption spectrum of the dye dissolved in ethanol has a large peak centered at 744 nm. The fluorescence exhibits a Stokes shift of approximately 36 nm with a lifetime of 1.7 +/- 0.3 ns. For dye laser pumping at 587 nm the laser threshold was 0.3 mJ, and the slope efficiency was 22% at the central lasing wavelength of 807 nm. The effect of various loss mechanisms is also discussed.

Method for complete determination of a refractive-index tensor by bireflectance: application to CdWO4.

The bireflectance effect is observed when a light beam is internally reflected in an anisotropic material. Generally, an unpolarized light beam splits into four beams on reflection. A new method for simultaneous measurement of the three refractive indices, based on laser-beam splitting due to bireflectance, is demonstrated in the biaxial CdWO4 crystal. The three principal refractive indices of CdWO4 were obtained in the visible range. At Lambda = 633 nm, nX = 2.09 +/- 0.01, nY - nX = 0.052 +/- 0.001, and nZ -nX = 0.114 +/- 0.002.