Abstract
Since the beginning of the Mars planet exploration, the characterization of carbon dioxide hypersonic flows to simulate a spaceship’s Mars atmosphere entry conditions has been an important issue. We have developed a Tunable Diode Laser Absorption Spectrometer with a new room-temperature operating antimony-based distributed feedback laser (DFB) diode laser to characterize the velocity, the temperature and the density of such flows. This instrument has been tested during two measurement campaigns in a free piston tunnel cold hypersonic facility and in a high enthalpy arc jet wind tunnel. These tests also demonstrate the feasibility of mid-infrared fiber optics coupling of the spectrometer to a wind tunnel for integrated or local flow characterization with an optical probe placed in the flow.
Highlights
Mars, with its carbon dioxide atmosphere, will probably be the planet visited by the human species
The optical bench built is in the form of a three channel spectrometer where two channels are used for calibration: on the one hand, the beam travels through a low pressure gas reference cell for absolute wavelength calibration, and on the other hand, the beam travels through a Fabry-Perot interferometer having 4.9 × 10−2 cm−1 free spectral range (FSR) for relative wavelength calibration
If we retain only the measurements for the first two milliseconds, this measurement campaign allows us to validate the feasibility of Tunable Diode Laser Absorption Spectroscopy (TDLAS) probing at 2.7 μm in this wind tunnel as well as the use of infrared fluorine fiber optics coupled to a miniature probe with short absorption path in the flow
Summary
With its carbon dioxide atmosphere, will probably be the planet visited by the human species. We are developing a new absorption spectrometer based on a recently available antimony diode laser [3] for CO and CO2 probing These diodes emit in the 2 to 3 μm spectral range where there are quite intense CO/CO2 lines for comfortable signal to noise ratio measurements under rarefied gas flow conditions. These lines are overlapped with atmospheric H2O lines absorbed outside the cell on a distance of about 1 meter. This is possible through current tuning but this restricts the spectral window to about 1 cm−1 wide allowing the monitoring of only one or two absorption lines
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