The infrared (IR) absorption and emission properties of Ho:KPC, Ho:KPB, and Ho:YAG were compared for possible applications in 2 µm laser cooling. Ho:KPC and Ho:KPB crystals were grown by vertical Bridgman technique using purified starting materials. A commercial Ho:YAG crystal was included in this study for comparison. Under resonant pumping at ~1.907 µm, the Ho-doped KPC/KPB crystals exhibited broad IR emission centered at ~2 µm based on the Ho³⁺ intra-4f transition ⁵I₇ → ⁵I₈. Under similar experimental conditions, Ho:YAG showed a narrow-structured emission band reflective of individual Stark levels. The average emission wavelength for Ho:YAG was determined to be ~2.03 µm. Initial heat loading/cooling experiments under ambient air were performed using a fiber laser operating at ~2.036 µm with an output power of 2 W. The Ho:KPC/KPB crystals exhibited small temperature increases of ~1.0 ºC. A significantly larger temperature increase of ~5 ºC was observed for Ho:YAG. IR transmission studies revealed the existence of OH impurities in the Ho-doped halides, which possibly lead to non-radiative decay channels.

Date Published: 10 March 2015
PDF: 7 pages
Proc. SPIE 9380, Laser Refrigeration of Solids VIII, 93800O (10 March 2015); doi: 10.1117/12.2077722

Published in SPIE Proceedings Vol. 9380:
Laser Refrigeration of Solids VIII
Richard I. Epstein; Denis V. Seletskiy; Mansoor Sheik-Bahae, Editor(s)