Compact Setup of a Tunable Heterodyne Spectrometer for Infrared Observations of Atmospheric Trace-Gases

We report on the development and characterization of the new compact infrared heterodyne receiver, iChips (Infrared Compact Heterodyne Instrument for Planetary Science). It is specially designed for ground-based observations of the terrestrial atmosphere in the mid-infrared wavelength region. Mid-infrared room temperature quantum cascade lasers are implemented into a heterodyne system for the first time. Their tunability allows the instrument to operate in two different modes. The scanning mode covers a spectral range of few wavenumbers continuously with a resolution of approximately ν ∆ν ≥ 10. This mode allows the determination of the terrestrial atmospheric transmission. The staring mode, applied for observations of single molecular transition features, provides a spectral resolution of ν ∆ν ≥ 10 and a bandwidth of 1.4 GHz. To demonstrate the instrument’s capabilities, initial observations in both modes were performed by measuring the terrestrial transmittance at 7.8 μm (∼ 1,285 cm−1) and by probing terrestrial ozone features at 8.6 μm (∼ 1,160 cm−1), respectively. The receivers characteristics and performance are described.