Abstract

A novel technique of high-resolution spectroscopy has been developed recently in our laboratory. We used a new version of the IR-mmwave double-resonance method to study CH3I in different vibrational states and to measure the frequency of rotational and vibrational transitions at sub-Doppler resolution.1 The method employs collinear propagation of pump and probe beams to select a narrow velocity class. In the experimental setup the intensity of the pump C02 laser is modulated by a mechanical chopper: when the laser is present, the absorption of microwaves is smaller because part of the molecules are removed from the lower state of the transition. The transmission of the mrawave radiation through the gas sample is measured with use of a synchronous amplifier referenced to the pump modulation.

© 1997 Optical Society of America