F. Raulin, D.M. Hunten, R.G. Knollenberg, M. Tacke, Y.L. Yung

The PIRLS Gas and Particle Spectrometer uses six narrow-bandwidth (0.001 cm^-1) tunable lead-salt diode lasers operating at 82 K, and scanning over typically 2 cm^-1 at selected, mid-infrared wavelengths (3-5 m m). These sources are directed over a 2-m open pathlength defined by a small reflector located 20 cm away, and extending over the edge of the Huygens Probe platform. Using proven techniques of laser absorption spectroscopy, which are simple in concept and easily calibrated, high sensitivities are readily achieved, and mole fractions as low as parts-per-billion (10^-9) will be measurable for several species of interest, a candidate suite of target gases being: the hydrocarbons CH₄, CH₃D, ¹³CH₄, C₂H₆, and C₂H₂; the nitriles HCN, and either C₂N₂ or HC₃N; and the oxygen-containing species CO, ¹³CO, C¹⁸O, and CO₂. Vertical profiles of gas concentrations will be determined from 30 suites of measurements from about 200 km in the stratosphere, down to the surface, with a vertical resolution of a fraction of the scale height (which is about 40 km).

"Tunable diode laser IR spectrometer for in situ measurements of the gas phase composition and particle size distribution of Titan’s atmosphere", CR Webster, SP Sander, R Beer, RD May, RG Knollenberg, DM Hunten, and J Ballard, Appl. Opt. 29, 907-917 (1990).

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