  We demonstrate a robust, carrier envelope phase (CEP)-stable, potassium
titanyl arsenate (KTA)-based optical parametric amplifier (OPA) delivering
6-cycle (79 fs), 3.8-$\mu$m pulses at a 100-kHz repetition rate with an average
power of 4.5 W. The pivotal achievement is stable generation of supercontinuum
(SC) seed pulses in a YAG crystal with a rather long pulse of 1.4 ps; to our
knowledge, this is the longest duration for SC generation (SCG). This
technology offers a robust and simplified OPA architecture with characteristics
of passively-stabilized CEP, simplified dispersion management with bulk
materials, wavelength tunability of the output pulses from 1.3-4.5 $\mu$m, and
the future power scaling up to kW-class based on Yb:YAG thin disk amplifiers.
The total output power of 17 W (signal plus idler) is achieved and the
capability of this high photon flux aspect is successively demonstrated by its
application to high harmonic generation (HHG) in ZnSe crystals, with which
faint yet novel signals above their bandgap are clearly observed.
