  We present a near-infrared optical parametric chirped-pulse amplifier (OPCPA)
and soft X-ray (SXR) high-harmonic generation system. The OPCPA produces
few-cycle pulses at a center wavelength of 800 nm and operates at a high
repetition rate of 100 kHz. It is seeded by fully programmable amplitude and
phase controlled ultra-broadband pulses from a Ti:sapphire oscillator. The
output from the OPCPA system was compressed to near-transform-limited 9.3-fs
pulses. High-power operation up to an average power of 35 W was achieved, and a
fully characterized pulse compression was recorded for a power level of 22.5 W,
demonstrating pulses with a peak power greater than 21 GW. We demonstrate that
at such high repetition rates, spatiotemporally flattened pump pulses can be
achieved through a cascaded second-harmonic generation approach with an
efficiency of more than 70%, providing a compelling OPCPA architecture for
power-scaling ultra-broadband systems in the near-infrared. The output of this
800-nm OPCPA system was used to generate SXR radiation reaching 190 eV photon
energy through high-harmonic generation in helium.
