THIS: a tuneable heterodyne infrared spectrometer for SOFIA

Abstract

The THIS instrument (Tuneable Heterodyne Infrared Spectrometer) is a versatile heterodyne receiver with a sensitivity close to theoretical prediction. It uses a Quantum Cascade Laser (QCL) as local oscillator and a HgCdTe photo-voltaic detector as mixer. The IF-spectrum is analyzed by means of a new broadband Acousto-Optical Spectrometer (AOS) with 3 GHz bandwidth and 1 MHz resolution. A dual sideband (DSB) system noise temperature has been measured with 2300 K at 10 μm wavelength, which is only 60% above the quantum limit. The stability of the system has been determined at an Allan variance minimum time of 50 seconds. Below this integration time the performance is purely radiometric. Also, the frequency stability has been measured with 1 MHz rms error within several hours. The quality of the instrument has been demonstrated by a few observing campaigns at the McMath-Pierce observatory on Kitt Peak. Measurements of Winds on Mars and Venus have been carried out and molecular line signals in sunspots have been detected. We propose to develop THIS as a second generation instrument for future astronomical observations on SOFIA.