High performance direct absorption spectroscopy of pure and binary mixture hydrocarbon gases in the 6–11 $$\upmu$$ μ m range

Abstract

× 10−3 cm −1 Hz −1∕2 it allows us to perform systematic measurements of hydrocarbon spectra of the first 7 alkanes under conditions which are not tabulated in spectroscopic database. We exemplify the system performance with measured direct absorption spectra of methane, propane, iso-butane, and a mixture of methane and propane.

High resolution quantitative multi-species hydrocarbon gas sensing with a cw external cavity quantum cascade laser based spectrometer in the 6–11 μm range

“…This procedure enables us to obtain spectra of an absolute accuracy of ± 0.001 cm -1 , which is much higher then reported before in Ref. [8].…”

“…A detailed description of the experimental setup and the measurement procedure has been published previously [8] to an acetylene absorption line with a nominal output of 1.523 µm ± 0.07 pm provides stable measurement conditions. The laser beam was split to allow coupling to the wavelength meter and to three MCT detectors (Vigo System, PVM-2TE-8).…”

“…Ref. [8]) This procedure could realize gapless coverage with a resolution of 0.001 cm -1 but implies long measurement times. For the results presented in this paper a few changes of the setup have been realized: the formerly 1 cm short path gas cell was replaced by a 10 cm path temperature controlled gas cell (cf.…”

“…In order to further improve the spectral measurement accuracy we replaced the germanium(Ge)-etalon in the setup from Ref. [8] by a custom-made air spaced etalon with wedged Ge windows. The one inch diameter windows are separated by a 10 cm hollow core Zerodur cylinder yielding a free spectral range (FSR) of 0.05 cm -1 or 1.5 GHz.…”

“…Quantitative spectroscopy of individual hydrocarbons as well as of their mixtures is of great interest for a multitude of applications. These include the detection of atmospheric composition change [1,2], pipeline gas leak detection [3], exhaled breath analysis [4,5] and especially the quantification of alkane mixtures in process streams [6][7][8] of the petrochemical industry. In the latter example gas chromatographs are the most widely employed technology for process analysis by decomposing the gas stream while measuring the concentration of each constituent [9].…”