A FAST-SCAN SUBMILLIMETER SPECTROSCOPIC TECHNIQUE

A new fast scan submillimeter spectroscopic technique (FASSST) has bee n developed which uses a voltage tunable backward wave oscillator (BWO ) as a primary source of radiation, but which uses fast scan (similar to 10(5) Doppler limited resolution elements/s) and optical calibratio n methods rather than the more traditional phase or frequency lock tec hniques. Among its attributes are (1) absolute frequency calibration t o similar to 1/10 of a Doppler limited gaseous absorption linewidth (< 0.1 MHz, 0.000 003 cm(-1)), (2) high sensitivity, and (3) the ability to measure many thousands of lines/s. Key elements which make this sy stem possible include the excellent short term spectral purity of the broadly (similar to 100 GHz) tunable BWO; a very low noise, rapidly sc annable high voltage power supply; fast data acquisition; and software capable of automated calibration and spectral line measurement. In ad dition to the unique spectroscopic power of the FASSST system, its imp lementation is simple enough that it has the prospect of impacting a w ide range of scientific problems. (C) 1997 American Institute of Physi cs.