Stabilization of femtosecond lasers for optical frequency metrology and direct optical to radio frequency synthesis.

We have actively stabilized the comb of frequencies from a mode-locked femtosecond laser using a Fabry-Perot reference cavity. This technique offers the ability to synthesize a comb of highly stable radio frequencies directly from optical transitions. The measured fractional frequency instability of the components of the frequency comb relative to the reference cavity was <5x10(-13) in 0.1 sec. The variation of the optical mode spacing versus frequency of the reference cavity was also directly measured using this technique.