  We introduce THz Stark spectroscopy by using intense single-cycle terahertz
pulses as the electric field source and monitoring the induced spectral
response of an isotropic molecular ensemble with a coincident femtosecond
supercontinuum pulse. THz Stark spectroscopy offers several advantages over
conventional Stark spectroscopy and opens previously inaccessible perspectives.
Most importantly, THz pulses oscillate faster than typical molecular rotations
and consequently eliminate the requirement to freeze the samples to prevent
poling effects. Hence, THz Stark spectroscopy allows for time-resolved studies
at arbitrary temperatures, specifically ambient conditions more relevant to
physiological or operative conditions. Moreover, dynamical field effects, e.g.,
higher order Stark contributions or hysteresis effects (non-Markovian
behavior), can be studied on the time scales of molecular vibrations or
rotations. We demonstrate THz Stark spectroscopy for two judiciously selected
molecular systems and compare the results to conventional Stark spectroscopy
and first principle calculations.
