A complete demonstration breadboard unit for advanced development as a high-TRL (technology readiness level) system has been constructed and characterized. Infusion of several new component technologies, such as ceramic:YAG material and high-power laser diode arrays (LDAs), combined with a proprietary minimal part count architecture, has resulted in dramatic performance gains. The proprietary dual-head configuration employs a pair of side-pumped laser slabs, optically in series in the cavity, but at opposing polarization orientations. This promises tremendous power range scalability, simplified and symmetrical thermal lens control, unprecedented stored energy extraction efficiency, and inherent diffraction limited TEM00 beam quality.

In addition, building upon the successful line of previous laser developments, the modular optical bench layout is designed for simple, in situ optical inspections, repeatability of builds, and ease of assembly. All of these characteristics have never before existed in a diodepumped solid-state laser (DPSSL) resonator.

Dividing a single, large laser head (laser slab) into a pair of smaller identical- gain modules gives the cavity high redundancy in the number of required laser diode arrays and laser slabs, as well as symmetrical thermal lens control, often difficult in side-pumped slab-based lasers. Each of the smaller slabs in the dual-head configuration is rotated 90° about the optical axis, as is the pumping configuration. By doing this, each slab produces a 1-axis positive thermal lens, but each of these “lenses” is orthogonal and, thus, easily corrected by adjusting the curvature of the HR cavity mirror. This technique, combined with an unstable resonator design and the use of a Gaussian reflective mirror (GRM) as its output coupler, creates a large TEM00 laser mode in the cavity without the use of hard apertures. This large mode, unobtainable without the GRM and unstable cavity geometry, efficiently overlaps the pumped gain regions in the slabs, and the efficiency is maximized. It was also found to be important to keep the individual components as accessible as possible, yet to retain precise hardware interconnections.

This work was done by Barry Coyle and Paul Stysley of Goddard Space Flight Center, and Demetrios Poulios of American University. GSC-16299-1

Photonics Tech Briefs Magazine

This article first appeared in the January, 2014 issue of Photonics Tech Briefs Magazine.

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