Generation of sub 50-fs Pulses at 920 nm by Frequency-Doubling using an Aperiodically-Poled Lithium-Niobate Crystal

Chirped-Pulse-Amplification (CPA) fiber-laser systems are well-established, robust and compact sources to generate femtosecond pulses; however, due to the limited gain bandwidth pulse durations directly obtained from such systems are limited to values >80 fs. We present a novel method to generate 45-fs pulses by frequency doubling the 109-fs pulses of a Thulium-doped CPA fiber-laser system. For this purpose we use spectral broadening near the quasi-phase-matching condition in an aperiodically poled crystal.