Crystal-length optimization in 681-nm pumped Tm:YAG and Tm:LuAG lasers: from record-low threshold to SESAM Q-switching
F. Kaya1, H. Bilici1, B. Sumpf2, U. Demirbas3,4, and E. Beyatli1
Published in:
Opt Commun, vol. 616, pp. 133364, doi:10.1016/j.optcom.2026.133364 (2026).
Abstract:
We systematically quantify how crystal length governs efficiency, tuning bandwidth, and passive Q-switching in 681 nm tapered-diode-laser (TDL) pumped Tm:YAG (1.5 at.%) and Tm:LuAG (2 at.%) oscillators. By scanning four lengths (3, 5, 7, and 9 mm), we identify a three-way trade-off among pump absorption, quasi-three- level reabsorption, and length-dependent passive loss. In continuous-wave (CW) operation, maximum extraction occurs at 7 mm in both hosts, while the Minimum absorbed lasing thresholds are obtained with the 3 mm crystals (35-45 mW). In the experiments, instantaneous slope efficiencies reach 60% (Tm:YAG) and 52% (Tm:LuAG), corresponding to photon-quantum efficiencies of 1.78 and 1.54. Using an intracavity quartz birefringent filter, we achieve >220 nm of continuous tuning and reproducible two-color operation; in Tm:LuAG, the longest crystals impose a short-wavelength cutoff (below ~1.92 µm), so shorter lengths are required for full spectral access. Passive Q-switching with a SESAM is strongest for 7 mm Tm:LuAG, producing 1.36 µs pulses with 1.2 W peak power. These results establish crystal- length selection rules for compact, red-pumped 2 µm sources balancing efficiency, tunability, and passive Q-switching.
1 Department of Electrical-Electronics Engineering, Recep Tayyip Erdogan University, Rize, 53100, Turkey
2 Ferdinand-Braun-Institut, Leibniz Institut für Höchstfrequenztechnik, D-12489 Berlin, Germany
3 Laser Technology Laboratory, Department of Electrical and Electronics Engineering, Antalya Bilim University, 07190 Antalya, Turkey
4 Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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