Long term (>500 seconds) phase coherence of a train of ultrashort pulses

Abstract

Following the recent demonstrations [1-4] of stabilizing the relative pulse-to-pulse phase between the carrier wave and the pulse envelope (carrier-envelope phase) generated by mode-locked femtosecond (fs) lasers, effort has focused on measuring and increasing the coherence time of this phase stability. Carrier-envelope phase stabilization is an important advance for fs technology, as the advent of few-cycle pulses makes it possible to study processes that are directly sensitive to the electric field of each pulse, rather than just the intensity envelope [5,6]. In order for most of these physical processes to be experimentally investigated, it is of interest to extend the time period (i.e., the coherence time) over which phase coherence of the carrier-envelope phase is maintained. By stabilizing the output of 10-fs mode-locked laser, we have increased the carrier-envelope phase coherence of the emitted pulse train from 1 ms [3] to greater than 500 seconds.