Sub-100 fs Kerr-lens mode-locked thin-disk lasers with novel Yb-doped gain media

The Yb-doped thin-disk laser is an ultrashort pulsed laser source with the highest average output power and pulse energy at present, due to its small thermo-optical distortion and nonlinear optical effects suppression. Although Yb:YAG has been widely used as a gain medium in thin-disk lasers, its narrow fluorescence bandwidth has limited availability of shorter pulses. Therefore, we are developing a thin-disk laser using a potassium double tungstate gain medium, Yb:KREW (Yb:KRE(WO4)2, RE = Y, Gd, Lu) for future applications to broadband ultrashort pulse laser oscillators and amplifiers. Yb:KREW is a promising group of gain media that combines a wide gain bandwidth and high gain coefficient, while they have drawbacks such as strong anisotropy in thermal and mechanical properties. In this study, we demonstrated the first Kerr lens mode-locked thin-disk laser operation with one of the tungstates gain media, Yb:KLuW by reducing anisotropic thermal distortion through low thermal resistance bonding techniques. Under OC transmittance of 0.6% and GDD-1400 fs2 conditions, the pulse duration of 48.9 fs and spectral bandwidth of 32.0 nm were demonstrated. This is the first KLM thin-disk laser demonstration of this material and its family (Yb-doped tungstate-based gain medium), and the pulse duration obtained was the smallest value using the same material reported so far. The average power, however, was limited to 425 mW by the low OC transmittance. In the future, through optimization of the cavity, further increases in power output are expected while maintaining the short pulse duration.