Abstract

Recently we achieved continuous-wave (cw) and Q-switched laser operation of Yb³⁺ in the disordered crystal Ca₃(NbGa)_2-xGa₃O₁₂ or shortly CNGG [1] previously studied only with Nd-doping [2] and Tm-doping [3]. It is an isotropic material similar to YAG and exhibits a rather high thermal conductivity of 4.7 Wm⁻¹K⁻¹, about one third of that of YAG which is much larger than for glasses. The disordered nature of the CNGG crystal provides several different lattice positions for the trivalent dopant ions, resulting in significant inhomogeneous broadening in the absorption and emission spectra. The maximum absorption cross section was measured to 3.3·10⁻²⁰ cm² at 973.5 nm. Apart from the zero-phonon line the maximum emission cross section is 2.5·10⁻²⁰ cm² at 1028 nm with a bandwidth of 21 nm (FWHM), roughly twice that of Yb:YAG. The measured fluorescence lifetime amounts to 791 µs. We demonstrated 2.0 W of cw output power with a slope efficiency of 40% for Yb:CNGG and the passively Q-switched operation delivered 1.35 W of average output power at a PRF of 16.7 kHz [1]. Here we demonstrate passive mode-locking of the disordered laser crystal Yb:CNGG using a semiconductor saturable absorber mirror (SESAM).

© 2009 IEEE