Indium-modified Yb:KLu(WO₄)₂ crystal: Growth, spectroscopy and laser operation

We report on the growth, spectroscopic and laser characterization of a novel monoclinic laser crystal, Yb,In:KLu(WO₄)₂ (Yb,In:KLuW). The absorption, stimulated-emission and gain cross-section spectra of 3.5 at% Yb, 5.5 at% In-doped KLuW are determined at room temperature with polarized light and compared with those for Yb,In:KYW, as well as singly Yb-doped KLuW and KYW crystals. It is found that the introduction of In results in a decrease of the transition cross-sections and in a spectral broadening of the absorption and emission bands. Such a broadening is more pronounced for light polarization E ||N_p. For Yb,In:KLuW, the maximum σ_abs is 9.9×10^–20 cm² at 980.9 nm for E ||N_m and the corresponding bandwidth of the absorption peak is 3.7 nm. The radiative lifetime for Yb³⁺ ions is 237±5 µs. The stimulated-emission cross-sections are σ_SE(m)=2.4×10^–20 cm² at 1022.4 nm and σ_SE(p)=1.3×10^–20 cm² at 1039.1 nm corresponding to an emission bandwidth of >30 nm and >35 nm, respectively. The diode-pumped N_g-cut Yb,In:KLuW microchip laser generated 4.11 W at 1042–1048 nm with a slope efficiency of 78%. The Yb,In:KLuW crystal is very promising for the generation of sub-100 fs pulses in mode-locked lasers due to its broadband emission characteristics.