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Proceedings Paper

Performances of Ho:YAG laser intracavity-pumped by a diode-pumped Tm:YLF laser
Author(s): Christelle Kieleck; Antoine Hirth; Martin Schellhorn
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Paper Abstract

Q-switched and diode-pumped 2 μm solid state lasers are becoming of increasing interest for efficient pumping of mid-infrared emitting optical parametric oscillators (OPOs). In particular, Thulium and Holmium rare earths seem to be most suited for systems with high efficiency due to their long upper state lifetime. Several works on Ho:YAG laser end-pumped by diode-pumped Tm:YLF laser have demonstrated high power operations. To simplify the set-ups, experiments with Tm-Ho intracavity lasers have been done; they demonstrated a 36.5% slope efficiency. Unfortunately these set-ups did now allow Q-switched operations and the thermal lens in the rods led to relatively poor beam quality (M2 ~ 5-6). We design an original intracavity configuration with a dichroic polarizing beamsplitter to decouple Tm:YLF and Ho:YAG cavities. This solution improves the beam quality and allows Q-switched operations. We obtained 1.9 W of 2.09 μm at the 17.3 W diodes pump level. The slope efficiency of the diode-pump to the Ho laser output and the optical-to-optical conversion efficiency achieved are respectively ~ 21.4% and ~ 11%. As anticipated, we experimentally scaled a shift of Tm:YLF emission from 1.908 to 1.953 μm that leads to an efficiency decrease for the Tm laser. In this intracavity geometry, Ho:YAG acted as a saturable absorber. Instead of a cw operation in free running, we observed random Tm:YLF laser pulses of ~ 2.5 μs that each resulted in a Ho pulse (~ 200-250 ns). When the acousto-optic modulator (AOM) worked, the Ho pulses did not follow the Q-switched frequency. In fact Ho emission depends on the Tm:YLF pump energy accumulated between two gates of the AOM. Possible ways to optimize the efficiency and avoid the passive Q-switching behaviour of Ho:YAG are suggested.

Paper Details

Date Published: 7 April 2004
PDF: 7 pages
Proc. SPIE 5478, Laser Optics 2003: Solid State Lasers and Nonlinear Frequency Conversion, (7 April 2004); doi: 10.1117/12.558350
Show Author Affiliations
Christelle Kieleck, French-German Research Institute ISL (France)
Antoine Hirth, French-German Research Institute ISL (France)
Martin Schellhorn, French-German Research Institute ISL (France)

Published in SPIE Proceedings Vol. 5478:
Laser Optics 2003: Solid State Lasers and Nonlinear Frequency Conversion
Vladimir I. Ustugov, Editor(s)

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