Abstract

The first demonstrations of carrier-envelope phase-stable few-cycle pulses lead to the demonstration of single attosecond pulse generation. This marked the starting point of a new research area of light-matter interactions, dubbed attoscience [1]. However, many experiments in this field require phase-stable pulses over long periods, and the scheme for phase-stabilization used in these pioneering experiments limited the period of time in which the experiment needed to be finished, since the feedback loops of the oscillator and amplifier were coupled. We demonstrate an improved scheme for phase stabilization, in which the feedback loops are independent. The second feedback loop, stabilizing the phase of the amplifier controls the dispersion in the prism-compressor in order to stabilize the phase. This improved scheme not only increases the time period over which phase-stable pulses can be provided, it provides as well a much smaller phase noise, see Fig. 1. After compressing the phase stabilized 25-fs output pulses from the amplifier to 5 fs in a hollow fiber - chirped mirror compressor, we use a fraction of the compressed output to measure the carrier envelope phase of the pulses with a phase-detector based on above threshold ionization (ATI) [2]. The response time of this detector is of the same order as the /-to-2/ interferometer used for phase stabilizing the amplifier output. Therefore, the detector can be used for an out-of-loop measurement to determine the quality of the phase stabilization, and as well to provide a feedback signal replacing the feedback generated with the/-to-2/interferometer, or for a third feedback loop. In Fig. 2 such an out-of-loop measurement is shown, yielding a RMS phase-jitter of 0.23 rad over a measurement period of 8 minutes. This proves that for other experiments, we can control the carrier-envelope phase with an accuracy better than π/10.

© 2007 IEEE