Abstract

We present to our knowledge the first passively mode-locked Yb:KGd(WO₄)₂(Yb:KGW) [1] laser. This diode-pumpable gain material is very suitable for high-power femtosecond lasers because it combines a broad amplification bandwidth (similar to Yb-doped glasses) with relatively large emission cross sections and good thermal properties. Using a setup (Fig 1) based on two high-brightness diode lasers at 980 nm and a semiconductor saturable absorber mirror (SESAM) as a mode locker, we obtain as much as 1.1 W average power in transform-limited soliton pulses (Fig 2) with 176fs duration at a center wavelength of 1037 nm. This performance makes the laser interesting for applications like three photon microscopy, nonlinear spectroscopy, or for pumping of optical parametrical oscillators At a repetition rate of 86 4 MHz the peak power is as high as 64 kW. The beam quality is close to diffraction-limited $\left({\text{M}}_{\text{tangential}}^2\approx 1.7,{\text{M}}_{\text{sagittal}}^2\approx 1\right)$. Mode locking is obtained over a tuning range from 1032 nm to 1058 nm. The shortest pulse duration we achieved is 100 fs at a center wavelength of 1051 nm with 200 mW average power Cw operation yields 13 W output power and a slope efficiency of 47% with regard to the power incident on the crystal.

© 2000 IEEE