Efficient 600-W-Laser Bars for Long-Pulse Pump Applications at 940 and 975 nm

• Published in: IEEE photonics technology letters Vol. 29; no. 19; pp. 1683 - 1686
• Main Authors: Karow, M. M., Frevert, C., Platz, R., Knigge, S., MaaBdorf, A., Erbert, G., Crump, P.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bars; Brightness; Calcium fluoride; Design optimization; Divergence; Energy conversion efficiency; Heat transfer; Laser cooling; Laser excitation; Layout; Measurement by laser beam; optical pumping; power conversion; power lasers; Pump lasers; Pumping; Resistance; Semiconductor laser arrays; Thermal resistance
• ISSN: 1041-1135; 1941-0174
• DOI: 10.1109/LPT.2017.2743242

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:CaF 2 -laser media at a power level of 600 W. The spatial brightness inferred (23 MW/cm 2 ×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 ηE > 60% (at 600 W), the latter exhibits low vertical divergence to enable low-loss external spectral stabilization at the zero-phonon line of Yb:CaF 2 (ηE = 50% at 600 W). The higher ηE 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.