Graphene mode-locked multipass-cavity femtosecond Cr4+: Forsterite laser

We report, for the first time to our knowledge, the use of graphene as a saturable absorber in an energy-scaled femtosecond Cr4+ : forsterite laser. By incorporating a multipass cavity, the repetition rate of the original short resonator was reduced to 4.51 MHz, which resulted in the generation of 100 fs, nearly transform-limited pulses at 1252 nm with a peak power of 53 kW. To the best of our knowledge, this is the highest peak power obtained from a room-temperature, femtosecond Cr4+ : forsterite laser mode locked with a graphene saturable absorber. The corresponding pulse energy was 5.3 nJ with only 24 mW of average output power. The saturation fluence and modulation depth of the GSA were measured to be 25 μJ/cm2 and 0.74%, respectively. The nonlinear effects in the Cr4+ : forsterite medium that limit further power scaling were also investigated by using different output couplers. © 2013 Optical Society of America