Interference of coherently scattered signals in the laser SRS-CARS monitoring of hydrogen concentration in gas mixtures |
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Authors: | G M Mikheev D G Kaluzhnyi A Yu Popov T N Mogileva |
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Institution: | (1) Institute of Applied Mechanics, Ural Division, Russian Academy of Sciences, Izhevsk, 426067, Russia |
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Abstract: | The possibility of measuring the hydrogen impurity concentration in dense gas mixtures by coherent anti-Stokes Raman scattering
(CARS) is studied. In this technique, biharmonic laser pumping based on stimulated Raman scattering (SRS) in compressed hydrogen
is used. Because of the interference between the coherent scattering components from buffer gas molecules and molecules of
the impurity to be detected, the signal recorded may depend on the hydrogen concentration by a parabolic law, which has a
minimum and makes the results uncertain. It is shown that this uncertainty can be removed if the frequency of the biharmonic
laser pump, which is produced by the SRS oscillator, somewhat differs from the frequency of molecular oscillations of hydrogen
in the test mixture. A sensitivity of 5 ppm is obtained as applied to the hydrogen-air mixture under normal pressure. The
coefficients of the nonresonance cubic hyperpolarizability of molecules and atoms are measured relative to nitrogen in a number
of gas media. |
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