Highly efficient and low threshold diode-pumped Kerr-lens mode-locked Yb:KYW laser.

We report a highly efficient diode-pumped femtosecond Yb:KYW laser with a compact three-element resonator. Near-transform-limited pulses of 107fs duration at a centre wavelength of 1056nm are produced at a pulse repetition frequency of 294MHz by utilising softaperture Kerr-lens mode locking. The femtosecond operation had a modelocking threshold at a pump power of 250mW and the laser was tunable from 1042nm to 1075nm. The optical-to-optical conversion efficiency exceeded 50% in this femtosecond-pulse regime.