Direct measurement and analysis of the carrier-envelope phase in light pulses approaching the single-cycle regime

Abstract

We demonstrate a solid-state device capable of providing direct information about the carrier-envelope (CE) phase of ultrashort (4 fs) laser pulses. The measurement is based on multi-photon-induced photoelectron emission from a gold surface. The amount of the charge emitted from the surface gives a clear indication of phase sensitivity, as predicted by our simulations and also by a simple intuitive model. This phenomenon was used to determine the CE phase value of each laser pulse in a mode-locked, unamplified, low-energy pulse train. The inability of the commonly used f-to-2f interferometric method to measure accurately extracavity drifts of the CE phase is discussed and contrasted with the direct phase measurement method proposed here. The evolution of the CE phase upon propagation of pulses comparable in duration to the optical cycle is analysed.