Observations with the Tuneable Heterodyne Infrared Spectrometer “THIS”

THIS (Tuneable Heterodyne Infrared Spectrometer) is a mid-infrared heterodyne receiver with sensitivity close to the theoretical quantum limit. A Quantum Cascade Laser (QCL) is used as local oscillator and a HgCdTe photovoltaic detector as mixer. The spectral information is derived from a broadband Acousto-Optical Spectrometer (AOS) with 3 GHz bandwidth and 1 MHz resolution. A dual sideband (DSB) system noise temperature has been found near 2400 K at 10 mum wavelength. The stability of the system has been determined at an Allan variance minimum time of 50 seconds. Very good frequency stability has been found with less than 1 MHz rms error within several hours. The quality of the instrument has been demonstrated during observing campaigns at the McMath-Pierce observatory on Kitt Peak and at the IRTF on Hawaii. Measurements of Winds on Mars and Venus are discussed as an example of the merits of THIS.