Fast sweep direct absorption (sub)millimeter-wave spectroscopy

Direct absorption spectroscopy has been the mainstay for spectral acquisition in the millimeter and submillimeter wavelength regimes because of the sensitivity offered by standard hot electron bolometer detectors. However, this approach is limited in its utility because of the slow spectral acquisition speeds. A few rapid acquisition techniques that offer reasonable levels of sensitivity have been developed, but these rely on specialized and costly equipment. We present here a new instrument design for a (sub)millimeter spectrometer that offers both rapid spectral acquisition and highly sensitive detection while using equipment from existing chirped-pulse Fourier transform spectrometers and direct absorption spectrometers. We report on spectrometer design and performance and compare the results to standard lock-in detection techniques.