Abstract

In the THz experiments discussed here, we have measured the absorption lineshapes in the ground state rotational bands of molecular vapors from resonance to frequency offsets as much as five times the resonant frequency and to as many as 200 linewidths away. Our measurements are well fit using a van Vleck-Weisskopf lineshape for an individual transition out to frequency offsets of the order of 1 THz. Further increasing the offset leads to a much reduced absorption compared with that of the van Vleck-Weisskopf lineshape. In fact, we find that at higher frequency offsets the measured absorption is almost an order of magnitude less than that given by the van Vleck-Weisskopf lineshape.

© 1997 Optical Society of America