Generation of above-terawatt 1.5-cycle visible pulses at 1 kHz by post-compression in a hollow fiber

We report on the generation of 6.1 mJ, 3.8 fs pulses by the compression of a kilohertz Ti:sapphire laser in a large-aperture long hollow fiber. In order to find optimal conditions for spectral broadening at high pulse energies, we explore different parameter ranges where ionization or the Kerr effect dominates. After identifying the optimum parameter settings, large spectral broadening at high waveguide transmission is obtained. The intense 1.5-cycle pulses are used for high-harmonic generation in argon and neon.