Generation of 7-fs pulses at 800 nm from a blue-pumped Optical Parametric Amplifier at degeneracy

Abstract

Optical Parametric Amplifiers (OPAs), thanks to their broad phase matching bandwidths, allow for the dramatic shortening of the duration of the driving pulse. In particular, OPAs pumped by the fundamental frequency (FF) or the second harmonic (SH) of Ti:sapphire and seeded by white-light continuum (WLC) enable the generation of few-optical-cycle pulses in a wide spectral range, from the visible [1] to the near-IR [2]. However the important spectral range around 800 nm has not yet been covered. In fact the WLC produced from an 800-nm driving pulse presents a highly structured amplitude and phase profile around the pump frequency. Previous attempts of amplification at 800 nm of a supercontinuum generated in a photonic crystal fiber resulted in ultra-broadband spectra, which were however not compressed due to the strong chirp on the seed pulses [3]. In this work we report on a two-stage approach for the generation of few-optical-cycle pulses at 800 nm; (i) a FF-pumped near-IR OPA produces pulses at 1.3 µm, which are used to generate a WLC with smooth spectral amplitude and phase characteristics around 800 nm; (ii) this WLC is amplified in a broadband SH-pumped OPA around degeneracy. The pulses are compressed to nearly transform-limited 6.8 fs duration by chirped mirrors.