  We report a 1 kHz repetition-rate mid-IR (MIR) optical parametric amplifier
(OPA) system operating at a central wavelength of 5.2 $\mu$m with the
tail-to-tail spectrum extending over 1.5 $\mu$m and delivering 40 $\mu$J pulses
that are compressed to 99 fs (5.6 optical cycles). Also we develop a novel
pulse compression scheme for further pulse compression and wavelength
tunability. As the first application of this laser system, we generated high
harmonics in bulk ZnSe above the bandgap, dense exciton generation after
10-photon absorption, high order sum- and difference-frequency generation,
ultrafast transition in the conduction band, which reflects the structure of
conduction bands.
