Temporal characterization of broadband, low-energy few-cycle pulses using surface third-harmonic generation dispersion-scan

By leveraging the intrinsically broadband surface third-harmonic generation (STHG) process, we implement a dispersion-scan [1] setup where the nonlinear medium is a simple sapphire plate and the generated third-harmonic signal is separated from the fundamental pulse spectrum by a pair of prisms and collected with a spectrometer. It is shown that although the pulses have relatively low energy (<2.5 nJ) for exciting third-order processes and the resulting nonlinear signal has significantly lower signal-to-noise ratio compared to standard second-harmonic generation, it enables the reliable temporal characterization of sub-8-fs, broadband few-cycle pulses by implementing a third-order variant of a recently introduced ptychographic pulse retrieval algorithm [2] .