Abstract

Carrier-envelope phase (CEP) control of mode-locked lasers has come of age, with recently demonstrated residual phase jitters approaching 10 mrad [1]. Such low jitter values could so far only be demonstrated with a novel feed-forward scheme [2] that relies on shifting the entire optical comb emerging from a mode-locked laser to zero offset frequency by means of an acousto-optic shifter. Compared to traditional feedback stabilization [3], the shifter based stabilization scheme has several advantages, including a larger effective servo bandwidth and a better long-term stability. However, feed-forward control also comes with several disadvantages, e.g., the angular dispersion of the stabilized output beam and side-effects emerging from a slow drift of the carrier-envelope (CE) frequency of the oscillator. Here we discuss an improved scheme that overcomes all the noted disadvantages. The method works only for amplified laser sources, but can tolerate even a rather massive drift of the CE frequency without any detrimental side effect. Moreover, the scheme can immediately be applied to the acousto-optic programmable dispersive filter (Dazzler), which suitably avoids the angular dispersion of acousto-optic shifters. Our improved scheme therefore constitutes a major step towards unconditional long-term CEP stabilization of amplified ultrafast laser systems.

© 2013 IEEE