Semiconductor-doped-silica saturable-absorber films for solid-state laser mode locking

We describe a new saturable-absorber materials system for solid-state laser mode locking based on thin, nonepitaxially grown, semiconductor-doped films. We fabricated thin films of InAs semiconductor microcrystalites in silica, using rf sputtering. We could control the linear absorption by varying the film thickness, and the nonlinear absorption saturation cross section and recovery time could be adjusted by use of rapid thermal annealing. The use of $30‐\mathrm{nm}‐\mathrm{thick}$ InAs-doped silica films on sapphire for initiation of Kerr-lens mode locking in a $\mathrm{Ti}:{\mathrm{Al}}_2{\mathrm{O}}_3$ laser was demonstrated. Pulses as short as 25 fs were generated with a wavelength tuning range from 800 to 880 nm.