Brian K. Brickeen

The temperature dependence of Nd/sup 3+/ doped solid-state lasers

The temperature-dependent performance for long-pulse and Q-switched Nd/sup 3+/ doped solid-state lasers are analyzed. Over a wide temperature range, it is shown that the output energy for the long-pulse laser decreases with increasing temperature as does that of the actively Q-switched laser when pumped to the same level of inversion at all temperatures. Conversely, when such lasers are pumped to the amplified spontaneous emission limit at each temperature or when the laser is passively Q-switched, the output energy increases with temperature. These temperature dependencies are analytically predicted and are compared to experimental results collected on various Nd:YAG and Cr:Nd:GSGG laser systems. The laser performance data and the model developed are shown to be in close agreement when using values for the stimulated-emission cross section and its temperature derivative obtained in separate spectroscopic measurements.

Laser performance of Yb 3+ doped oxyorthosilicates LYSO and GYSO

Ytterbium offers a number of advantages as the active ion in solid-state laser crystals, but is hindered by the disadvantages of a three level lasing scheme. Yb(3+)-doped oxyorthosilicates have emerged in recent years as potentially quasi-four level laser materials. Two such crystals, Yb:GdYSiO(5) and Yb:LuYSiO(5), are investigated to determine the extent of four-level behavior. It is shown that these crystals demonstrate a significant reduction in the pump intensity required to reach threshold, but still exhibit three-level effects in terms of self-absorption, population inversion, and thermal sensitivity. The important material properties such as the coefficient of thermal expansion and the thermo-optic coefficient are measured.

Thermal lens shaping in Brewster gain media: A high-power, diode-pumped Nd:GdVO 4 laser

A straightforward method is presented for generating a stigmatic spherical thermal lens in laser-diode-pumped, Brewster-cut solid-state gain media by shaping the aspect ratio of the elliptical pumped region. Demonstration of this laser head design with Nd:GdVO(4) as the gain medium yields a stable, efficient, high-power (>20W) diode-pumped laser at 1063nm. Analysis of the spatial mode characteristics of a 67cm-long symmetric resonator both confirms the radially symmetric nature of the pump-induced thermal lens and indicates that laser resonators incorporating this head design can readily generate a high spatial beam quality (M(2) < 2).

Laser resonator design using optical ray tracing software: comparisons with simple analytical models and experimental results

Software simulation of complex resonator and optical system designs offer the potential to couple traditional opto/mechanical tolerance analysis with the required system performance. One such a software platform, ASAP, and the methodology to perform tolerance analyses has been evaluated and validated for the case of the crossed Porro resonator. Simulation results and experimental measurements are presented and discussed.

High energy microlaser and compact MOPA transmitter

A compact micro-oscillator incorporating a dual-bounce, grazing incidence gain module with a folded resonator cavity is presented. The gain module, previously developed for Nd:YVO4, is embodied in highly doped ceramic Nd:YAG to generate improved Q-switch performance while maintaining localized pump absorption. The cavity design utilizes a doubly folded optics path around the gain crystal to increase the intra-cavity mode for a more optimum overlap with the pump light volume produced by standard lensed laser diode bars. A modified CS-package diode mount is developed to facilitate the reduced size of the oscillator without sacrificing the ability to use a high-energy, side-pumping arrangement. The oscillator is combined with a high gain, high energy extraction VHGM amplifier to generate a transmitter source on the order of 50 mJ. Cooling for both the oscillator and amplifier modules is provided via a conductive path through the base of the package. Both devices are mounted on opposite sides of a phase-change cooling reservoir to enable self-contained, burst-mode operation. Beam shaping of the oscillator output, in preparation for injection into the amplifier, is contained in a small cut-away path on the reservoir side.

Athermal emission in Yb,Er:glass

We report on the temperature dependent spectroscopic properties of Yb(3+) and Er(3+) co-doped glass gain media in the eye-safe spectral region. Measurements suggest that judicious selection of the operating wavelength can lead to a laser output with minimal dependence on the temperature of the gain medium.

Coupling 4 W cw from a diode-pumped Nd:YAG laser through a 5-μm-core single-mode fiber

As one approach to retrofitting a reprographic writing engine with a higher-power laser for direct-to-plate imagesetting, we developed a single-mode-fiber delivery for a Nd:YAG laser. The writing process required 4 W cw in a high-quality beam capable of high-speed modulation. We developed a laser of adequate beam quality and a fiber-coupling system that met the requirement with emission of 4 W cw at 1064 nm wavelength from a 5 micrometers -core fiber that had a 950 nm wavelength cutoff for the second mode.