  We report on the generation of 6.1 mJ, 3.8 fs pulses by the compression of a
kHz 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.
