  We studied the effects of cryogenic cooling of a 2-[3-(4-hydroxystyryl)-5,
5-dimethylcyclohex-2-enylidene] malononitrile (OH1) crystal on the generation
of broadband THz pulses via collinear optical rectification of 1350 nm
femtosecond laser pulses. Cooling of the OH1 crystal from room temperature to
10 K leads to a ~10% increase of the pump-to-THz energy conversion efficiency
and a shift of the THz pulse spectra to a higher frequency range. Both effects
are due the temperature variation of THz absorption and the refractive index of
the OH1 crystal. This conclusion has been verified by temperature dependent
measurements of the linear absorption in the THz frequency region.
