Tunable Yb:CaF₂-SrF₂ laser and femtosecond mode-locked performance based on semiconductor saturable absorber mirrors

We experimentally demonstrate an effective continuous-wave tunable operation and femtosecond passively mode-locked pulse from a Yb:CaF₂-SrF₂ mixed crystal laser for the first time. Pumped by a 977 nm fiber-coupled laser diode, a continuous-wave mode-locked pulse as short as 634 fs was generated. The shortest pulse operated under a repetition rate of 87 MHz at the central wavelength of 1047 nm. The calculated time-bandwidth product was 0.503, which was 1.6 times the Fourier transform-limited sech²-shaped pulses.