Gain-guided beam-quality evolution in high-energy 589 nm KGW Raman lasers with cascaded third-Stokes conversion

Résumé fourni par la source

High-energy Raman lasers in plane-mirror cavities scale pulse energy easily but degrade in beam quality, and the responsible mechanisms have not been experimentally separated. We report a 10 Hz, 532 nm-pumped 589 nm KGW Raman laser that disentangles pump-defined gain guiding from cascaded third-Stokes depletion. At 2.3 W average pump power the estimated thermal focal length exceeded 10 m against a 150 mm cavity, so gain guiding dominated. Increasing the pump diameter from 2.8 to 4.0 mm scaled the 589 nm energy from 53.8 to 101.2 mJ, while M x 2 / M y 2 degraded from 13.21/13.56 to 30.00/28.75. At equal output energy a larger aperture consistently gave poorer beam quality, isolating gain-guided multimode competition as the primary cause. Near third-Stokes saturation, intensity-dependent depletion was also correlated with a transient M 2 reduction. The 101.2 mJ output raises the brightness figure of merit E /( M x 2 M y 2 ) to 0.117 mJ, about 3.3 times the 0.035 mJ of the previously reported comparable-energy result ( M 2 ≈ 65), giving a practical energy-beam-quality criterion.

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