Towards a Sub-9 fs, 3 mJ, CEP-Stable Multipass Ti:Sapphire Amplifier

Summary form only given. We present an efficient, single-stage ultrabroadband, CEP-stable multipass Ti:Sa amplifier. The system generates sub-13 fs, 3.2mJ laser pulses at a repetition rate of 1kHz [1]. The excellent long-term CEP stability of sub-150 mrad rms noise (75 h measurement, single shot, every shot data acquisition) was achieved by the combination of the feed-forward CEP stabilization technique for the seed-oscillator [2] with the single-shot CEP measurement of the amplified laser pulses at 1 kHz and a fast feedback which corrects for the CEP drift in the amplifier via an RF phase shifter [3]. In order to achieve (spectrally) ultrabroadband laser pulses supporting a sub-13 fs pulse duration, custom Gaussian filters in combination with an acousto-optic programmable dispersive filter (AOPDF Dazzler, Fastlite) are used to suppress the gain-narrowing process in the amplifier. Due to the large spectral bandwidth of FWHM > 130 nm, it was possible to further broaden the spectrum (and, therefore, to reduce the pulse duration) via a moderate self-phase modulation (SPM) process in bulk material. After the grating compressor, a telescope with a curved focusing mirror and a concave defocusing lens was used to decrease the beam size of the laser pulses. Here the lens acts as the nonlinear SPM medium. The pulses are afterwards compressed using chirped mirrors.