Control over absolute carrier-envelope phase of ultrafast pulses:complete waveform synthesis

Abstract

Recent demonstrations [1, 2, 3, 4] of stabilizing the relative pulse-to-pulse phase between the carrier wave and the pulse envelope (carrier-envelope phase or the pulses’ ”absolute phase”) generated by mode-locked femtosecond lasers have established the groundwork for synthesizing electric fields with known amplitude and absolute phase at optical frequencies. However, in order to take advantage of this capability and experimentally investigate physical processes that are dependent on the electric field, rather than just the intensity envelope of the pulse [5], at least two additional steps are necessary. Increasing the coherence time of the pulses’ absolute phase is a crucial first step as it effectively determining the ”lifetime” of the synthesized electric field. In addition, the previously mentioned work [1, 2, 3] has stabilized the change of the absolute phase from pulse to pulse. To truly synthesize electrical fields, the value of the absolute phase must be measured and ultimately set to a prescribed value. In this work we address both of these issues. By refining our feedback loops used to stabilizing the output of a 10-fs Ti:Sapphire laser and increasing the mechanical stability of the laser and the associated optics, we have increased the absolute phase coherence of the emitted pulse train to greater than 5 minutes. We will also discuss techniques and experimental results of measuring the pulse train’s absolute phase as emitted directly from the laser itself.