High-repetition-rate femtosecond pulse generation in the blue

We report the generation of high-repetition-rate femtosecond pulses in the blue by intracavity doubling of a mode-locked Ti:sapphire laser using β-BaB2O4. To reduce the pulse-broadening effect of group-velocity mismatch, an extremely thin β-BaB2O4 crystal is used. By pumping the Ti:sapphire laser with 4.4 W of power from an Ar+ laser, as much as 230 mW of 430-nm light is produced at a 72-MHz repetition rate and a 89-fs pulse width. This represents an effective conversion efficiency of ~75% from the typical infrared output to the second harmonic. Pulse widths as short as 54 fs are achieved for the blue output.