  Transmission through photoexcited semiconductors is used to temporally and
spectrally shape a Terahertz pulse. By adjusting the optical pump-THz probe
delay, we experimentally introduce a polar asymmetry in the pulse profile as
high as 92%. To shape the spectrum, we apply the same technique after strongly
chirping the Terahertz pulse. This led to significant reshaping of the spectrum
with a 52% upshift of spectrum median. Pulse shaping techniques introduced here
are of particular importance for temporal and spectral shape-sensitive THz
nonlinear experiments.
