Dusan Stupar

Direct observations of Venus upper mesospheric temperatures from ground based spectroscopy of CO2

[1] We report direct observations of temperatures in the Venus upper mesosphere around 110 km altitude (0.15 Pa). Information about temperatures at these altitude regions are sparse especially for the dayside of Venus. Data was acquired during three observing campaigns between March and June 2009 at the McMath-Pierce Solar Telescope of the National Solar Observatory on Kitt Peak, Arizona, using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS). The linewidths of fully resolved non-thermal emission lines in the 10.6 μm band of CO 2 were used to derive temperatures on the Venus dayside. Temperatures were measured with high spatial resolution at 115 positions on the Venus dayside between 67°N and 90°S and various offsets from the apparent discs central meridian longitude (CML) providing the first extensive dataset for the dayside mesosphere. The retrieved temperatures show a strong local time and latitude dependence. Values of 160 K are observed close to the terminator and at the South pole while temperaturs reach 250 K at the sub solar point. These high values are in disagreement with the predictions of the Venus International Reference Atmosphere model but are consistent with earlier measurements from 2007.

Fully reflective external-cavity setup for quantum-cascade lasers as a local oscillator in mid-infrared wavelength heterodyne spectroscopy

To our knowledge we present the first experiments with a fully reflective external-cavity quantum-cascade laser system at mid-infrared wavelengths for use as a local oscillator in a heterodyne receiver. The performance of the presented setup was investigated using absorption spectroscopy as well as heterodyne techniques. Tunability over approximately 30 cm(-1) at 1130 cm(-1) was demonstrated using a grating spectrometer. A continuous tuning range of 0.28 cm(-1) was verified by observing the spectra of an internally coupled confocal Fabry-Pérot interferometer and the absorption lines of gas phase SO(2). In a second step the output from the system was used as a local oscillator signal for a heterodyne setup. We show that spectral stability and side mode suppression are excellent and that a compact external-cavity quantum-cascade laser system is well suited to be used as a local oscillator in infrared heterodyne spectrometers.

Probing Stellar Atmospheres with Ultra‐High Resolution Infrared Heterodyne Spectroscopy

We present astronomical applications of the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS). Measurements of planetary atmosphere dynamics of Mars and Venus with an accuracy of <10 m/s, taken over the last two years, demonstrate the capabilities of heterodyne spectroscopy in the mid infrared.High spectral resolution of up to R = 107 enables us to fully resolve molecular or atomic lines and to deduce three dimensional structures. Precise measurements of stellar winds are also feasible with THIS. Furthermore, large scale convection in stellar atmospheres might be a target for ultra‐high resolution spectroscopy. Other possible applications include the measurement of stellar magnetic fields by observing the Zeeman splitting of molecular lines (e.g. Mg I), or velocity resolved observations of Ne II in circumstellar discs.

THIS: a tuneable heterodyne infrared spectrometer for SOFIA

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.