Growth and properties of KLu(WO₄)₂, and novel ytterbium and thulium lasers based on this monoclinic crystalline host

TLDR

High‑quality monoclinic KLu(WO₄)₂ crystals (KLuW) were grown, enabling advances in Yb³⁺ and Tm³⁺ spectroscopy and laser operation. The study reviews KLuW growth and characterizes its structural, thermo‑mechanical, and optical properties while presenting laser performance under Ti:sapphire and diode pumping. Growth of bulk and epitaxial KLuW crystals, measurement of their structural, thermo‑mechanical, optical, and spectroscopic properties, and laser operation using Ti:sapphire and diode pumping at 980 nm and 800 nm were performed. The authors achieved CW slope efficiencies of ≈57 % (bulk) and ≈66 % (epitaxial) Yb:KLuW lasers under Ti:sapphire pumping, 3.28 W output with 78 % slope efficiency under diode pumping, Q‑switched operation at 1031 nm with 32.4 µJ pulses and Raman conversion to 1138 nm, 81 fs and 114 fs mode‑locked pulses, and a diode‑pumped Tm:KLuW laser reaching 4 W at 1950 nm with 69 % slope efficiency and tunability from 1800 to 2039 nm.

Abstract

Abstract High‐quality crystals of monoclinic KLu(WO 4 ) 2 , shortly KLuW, were grown with sizes sufficient for its characterization and substantial progress was achieved in the field of spectroscopy and laser operation with Yb 3+ ‐ and Tm 3+ ‐doping. We review the growth methodology for bulk KLuW and epitaxial layers, its structural, thermo‐mechanical, and optical properties, the Yb 3+ and Tm 3+ spectroscopy, and present laser results obtained in several operational regimes both with Ti:sapphire and direct diode laser pumping using InGaAs and AlGaAs diodes near 980 and 800 nm, respectively. The slope efficiencies with respect to the absorbed pump power achieved with continuous‐wave (CW) bulk and epitaxial Yb:KLuW lasers under Ti:sapphire laser pumping were ≈ 57 and ≈ 66%, respectively. Output powers as high as 3.28 W were obtained with diode pumping in a simple two‐mirror cavity where the slope efficiency with respect to the incident pump power reached ≈ 78%. Passively Q‐switched laser operation of bulk Yb:KLuW was realized with a Cr:YAG saturable absorber resulting in oscillation at ≈ 1031 nm with a repetition rate of 28 kHz and simultaneous Raman conversion to ≈ 1138 nm with maximum energies of 32.4 and 14.4 μJ, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode‐locking by a semiconductor saturable absorber mirror (SESAM) produced bandwidth‐limited pulses with duration of 81 fs (1046 nm, 95 MHz) and 114 fs (1030 nm, 101 MHz) for bulk and epitaxial Yb:KLuW lasers, respectively. Slope efficiency as high as 69% with respect to the absorbed power and an output power of 4 W at 1950 nm were achieved with a diode‐pumped Tm:KLuW laser. The slope efficiency reached with an epitaxial Tm:KLuW laser under Ti:sapphire laser pumping was 64 %. The tunability achieved with bulk and epitaxial Tm:KLuW lasers extended from 1800 to 1987 nm and from 1894 to 2039 nm, respectively.