A Wide Spaced Femtosecond Ti:Sapphire Frequency Comb at 15 GHz by a Fabry—Pérot Filter Cavity

We realize a wide spaced frequency comb by using an external low-fineness Fabry-Perot (F-P) cavity to filter few-cycle laser pulses from a Kerr-lens mode-locked Ti:sapphire laser at the fundamental repetition rate of 350 MHz. Mode spacing as wide as 15 GHz with spectrum covered from 690 nm to 710 nm is demonstrated, corresponding to a filter multiple of about 43. The scanning transmission peaks after the F-P cavity with cavity lengths are also simulated numerically, and the results are in agreement with the experiment.