Impact of atmospheric clutter on Doppler-limited gas sensors in the submillimeter/terahertz.

It is well known that clutter (spectral interference) from atmospheric constituents can be a severe limit for spectroscopic point sensors, especially where high sensitivity and specificity are required. In this paper, we will show for submillimeter/terahertz (SMM/THz) sensors that use cw electronic techniques the clutter limit for the detection of common target gases with absolute specificity (probability of false alarm ≪ 10⁻¹⁰) is in the ppt (1 part in 10¹²) range or lower. This is because the most abundant atmospheric gases are either transparent to SMM/THz radiation (e.

Submillimeter spectroscopy for chemical analysis with absolute specificity.

A sensor based on rotational signatures in the submillimeter (SMM) region is described. This sensor uses frequency synthesis techniques in the region around 10 GHz, with nonlinear diode frequency multiplication to 210-270 GHz. This provides not only a nearly ideal instrument function, but also frequency control and agility that significantly enhance the performance of the spectrometer as a sensor.