Parts-per-million water vapor sensing using an ultrahigh-Q THz disc microresonator

Abstract

We report on the first demonstration of a THz gas spectrometer using a sub-wavelength thick ultrahigh-Q THz disc microresonator. Leveraging the microresonator's ultrahigh quality factor in excess of 120,000 and the intrinsically large evanescent field, allows for the implementation of a very compact spectrometer without the need for complex multi-pass gas cells. Water vapor concentrations as low as 4 parts per million at atmospheric conditions have been readily achieved in these proof-of-concept experiments.