Novel ytterbium and thulium lasers based on the monoclinic KLu(WO4)2 crystalline host

High-quality crystals of KLu(WO4)2, shortly KLuW, were grown with sizes sufficient for characterization of the thermomechanical and optical properties, and substantial progress was achieved in the field of spectroscopy and laser operation with Yb3+- and Tm3+-doping. We review the properties of flux grown KLuW, the Yb3+ and Tm3+ 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 &mgr;J, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode-locking by a semiconductor saturable absorber mirror (SESAM) resulted in 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 tunability of this laser, under Ti:sapphire laser pumping, extended from 1800 to 1987 nm. An epitaxial Tm:KLuW laser provided slope efficiency as high as 64% and a tuning range from 1894 to 2039 nm when pumped by a Ti:sapphire laser.