Sub-50-fs Kerr-lens mode-locked Yb:GdYCOB laser

Yb 3+ (Yb)-doped monoclinic oxoborates Ca 4 REO(BO 3 ) 3 where RE stands for Gd or Y (denoted as GdCOB and YCOB, respectively) feature the advantages of extremely flat and smooth gain profile due to the significant inhomogeneous broadening related to their disordered structure, large ground state splitting of >1000 cm -1 , good thermo-optic properties as well as polarized emission due to the natural birefringence (acentric monoclinic symmetry), which makes them attractive for the development of tunable and sub-100-fs solid-state lasers in the 1-μm spectral region [1] - [3] and self-frequency doubling. In mixed Yb:Ca 4 Gd x Y 1-x O(BO 3 ) 3 (shortly Yb:GdYCOB) crystal with a partial substitution of Y 3+ by Gd 3+ ions is expected to provide additional broadening of the spectral bands due to the compositional disorder [4] , [5] . Here, we report on a Kerr-lens mode-locked (KLM) operation of Yb:GdYCOB laser generating pulses as short as 43 fs with an average power of 84 mW at 1036.5 nm and a pulse repetition rate of ~70 MHz.