Optical frequency stabilization of a 10 GHz Ti:sapphire frequency comb by saturated absorption spectroscopy in 87rubidium

The high power per mode of a recently developed 10 GHz femtosecond Ti:sapphire frequency comb permits nonlinear Doppler-free saturation spectroscopy in Rb with a single mode of the comb. We use this access to the natural linewidth of the rubidium D2 line to effectively stabilize the optical frequencies of the comb with an instability of 7 10−12 in 1 s of averaging. The repetition rate is stabilized to a microwave reference leading to a stabilized and atomically referenced comb. The frequency stability of the 10 GHz comb is characterized using optical heterodyne with an independent self-referenced 1 GHz comb. In addition, we present alternative stabilization approaches for high repetition rate frequency combs and evaluate their expected stabilities.