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Self-referencing of optical frequency combs

Stabilization of the carrier envelope phase (CEP) drift of femtosecond oscillators has found widespread application in frequency metrology and high-field nonlinear optics and is one of the most important prerequisites for attophysics. To date, CEP stabilization of laser oscillators exclusively relies on phase coherent locking of the measured carrier-envelope frequency fCE to a reference oscillator. Servo locking the CEP therefore unavoidably involves feedback into the laser, which may generally give rise to several undesired side effects [1]. First, closing the feedback loop and changing the intracavity CEP is virtually not accomplishable without also affecting output power and cavity roundtrip time. Second, the servo loop requires a rather complex locking electronics. Finally, it is impossible to directly produce a pulse train with constant CEP (fCE =0) with the traditional locking scheme. In the following, we will present a novel self-referenced frequency comb synthesis scheme that overcomes all three inconveniences and is directly applicable to a femtosecond laser oscillator.