M.M. Karow, C. Frevert, R. Platz, S. Knigge, A. Maaßdorf, G. Erbert, and P. Crump

Published in:

IEEE Photonics Technol. Lett., vol. 29, no. 19, pp. 1683-1686 (2017).

Abstract:

We report the first demonstration of 1.2 J-emission into long pulses (≥2 ms) from passively cooled laser bars. These efficient high-fill-factor bars were developed for long-pulse pumping of Yb:CaF₂-laser media at a power level of 600 W. The spatial brightness inferred (23 MW/cm²×sr) exceeds the state of the art. The bars are based on an extreme-double-asymmetric and an extremely-low-vertical-divergence epitaxial design for pumping at 940 and 975 nm, respectively. While the first design is optimized for high power-conversion efficiency η_E > 60% (at 600 W), the latter exhibits low vertical divergence to enable low-loss external spectral stabilization at the zero-phonon line of Yb:CaF₂(η_E = 50% at 600 W). The higher η_E at 940 nm and lower thermal resistance due to its vertical structure improve the lateral farfield, increasing the brightness by nearly 50% over the 975 nm-structure. We varied the lateral layout comprising 186, 400, and 1200 µm-stripes at 70% fill-factor. The smaller stripes revealed the highest brightness, while the degree of polarization increases by 5% using wider stripes.

Index Terms:

Semiconductor laser arrays, power conversion, optical pumping, power lasers, brightness.

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