Low-threshold, room-temperature femtosecond Cr4+:forsterite laser

We describe a low-threshold Cr(4+):forsterite laser which can be operated in continuous-wave as well as Kerr-lens mode-locked regimes at room temperature. To achieve low lasing thresholds, a 3-mm-long Cr(4+):forsterite crystal with a single-pass absorption of 41% was used to reduce the passive losses. Furthermore, a thin crystal was used to minimize the pump induced thermal gradients. During continuous-wave operation, absorbed threshold pump powers as low as 290 mW were obtained at 200C in single-pass pumping with a Yb fiber laser. To the best of our knowledge, this is the lowest pump threshold reported to date for Cr(4+):forsterite lasers. Furthermore, Kerr-lens mode locking could also be obtained using dispersion compensation with double-chirped mirrors. With an input pump power of 3 W, nearly transform-limited 89-fs pulses were obtained at a repetition rate of 200 MHz and with an average output power of 85 mW.