Efficient continuous-wave and passive Q-switched mode-locked Er : CaF-SrF lasers in the mid-infrared region.

An Er-doped CaF-SrF mixed crystal was grown using the temperature gradient technique, and its laser characteristics were studied. In a compact linear cavity, a continuous-wave output power of 712 mW was obtained with the highest slope efficiency of 41.4%. Using a semiconductor saturable absorber mirror, a passive Q-switched mode-locked Er:CaF-SrF laser emitting at 2729.5 nm was demonstrated for the first time, to the best of our knowledge. The maximum average output power of 125 mW was obtained at an absorbed pump power of 1.81 W, and the repetition rate of the Q-switched envelope was 4.17 kHz. The mode-locked pulses in the Q-switched pulse envelope had a repetition rate of 136.3 MHz, and its duration was estimated to be approximately 1.78 ns. These results indicate that the Er-doped CaF-SrF mixed crystal is promising for the development of an ultrafast laser in the mid-infrared regime.