William H. Long

Brightness-Scaling Potential of Actively Phase-Locked Solid-State Laser Arrays

Recent progress in developing phased arrays of high-brightness solid-state lasers is summarized. We address the prospects for continued brightness-scaling via a model that extrapolates measured results to large numbers of array elements and provides a quantitative illustration of the features of coherent beam combination. This demonstrates that with present-day technology, both slab and fiber lasers have the capability to scale to unprecedented brightness levels.

Beam cleanup and low-distortion amplification in efficient high-gain hydrogen Raman amplifiers

We report the results of a theoretical and experimental investigation of two important properties of Raman converters. The first property is Raman beam cleanup, which refers to the generation of high-quality Stokes beams in a Raman amplifier pumped by laser beams of poor spatial quality. The second is nearly distortion-free amplification of aberrated Stokes beams in a Raman amplifier pumped by good-quality laser beams. A parallel beam geometry was used with collinear pump and Stokes beams. In both cases, excellent energy-conversion efficiencies into the first Stokes order, of the order of 60%, were demonstrated at high amplifier gains of 100 to 1000. The spatial characteristics of the amplified beams were found to be in good agreement with model predictions.

Noncritically phase matched mid-infrared generation in AgGaSe/sub 2/

A tunable mid-infrared optical parametric oscillator has been demonstrated using a noncritically phase matched AgGaSe/sub 2/ crystal with pump wavelength tuning. Average power experiments have generated several hundred milliwatts of 2.63 and 3.71 /spl mu/m radiation using a high-repetition-rate, multiwatt 1.54 /spl mu/m pump source. Interferometric measurements of the AgGaSe/sub 2/ crystal during operation indicated only minor thermal lensing. >

Infrared laser heating for studies of cellulose degradation

We describe a new technique for studying thermally induced chemical transformations in cellulose. The apparatus consists of a carbon dioxide laser for heating, an IR thermometer, and an optical reflectance spectrometer for tracking the progressive discoloration of the sample. To illustrate the technique, we present measurements from a single piece of sample linen along five isotherms in the 200-290 degrees C range. We derive an algebraic expression for the reflectivity of the sample as a function of the areal concentrations of the chromophoric states produced at temperature. The results are then explained in terms of first-order chemical rate theory and a four-step model. From the measurements we derive the activation energies, Arrhenius constants, and reflectivities of the chromophoric states.

19-kW Phase-locked MOPA Laser Array

We have developed a scalable architecture of phase-locked Nd:YAG master oscillator power amplifiers. In cw operation a 2×1 array emitted 19.0 kW with 30% optical efficiency and average beam quality of 1.73 × diffraction-limited.

High power scalable Nd:YAG laser architecture

Under the Joint High Power Solid-State Laser (JHPSSL) program, Northrop Grumman is developing a laser architecture that can scale to >100 kW with a near-term goal of a 25 kW demonstration. The laser concept uses a single master oscillator to drive parallel power-amplifier chains; output from the amplifier chains are tiled and phased (piston corrected) to provide a spatially coherent beam. Scaling is achieved by adding parallel amplifier chains.

Transverse-pumped multiple diode bar Tm:YAG laser

We have constructed a laser utilizing five 10 W cw diode bars to transverse-pump a Tm:YAG rod in a multiple-pass pump cavity. At an estimated rod temperature of 35 - 40 degree(s)C, 6.0 W of multi-mode and 3.8 W of single-mode output were obtained at 2.02 micrometers in a non- optimized resonator with 50 W incident pump power.

Quasi-phase-matched Harmonic Generation In Gallium Arsenide And Zinc Selenide Single-crystal Plates

We report a novel quasi-phase-matched (QPM) wavelength converter structure based on total-internal-reflection (TIR) zig-zag paths in polished plane-parallel slabs of single-domain GaAs and ZnSe crystals.