Application of raman scattering of light for determining the vibrational-level populations of nitrogen in a nonequilibrium gas-dynamic current

We describe an experimental apparatus and method for measuring the vibrational temperature of nitrogen and the density of particles in a gas-dynamic current of a С02—N2—Не mixture through the use of Raman scattering of light. Raman scattering is excited by the second harmonic of an yttrium aluminum garnet-neodymium laser (λ$_{L}$ = 532 nm) inside a multipass cuvette with the number of light passes ~50. The useful signals of the Stokes and anti-Stokes components of the scattering are discriminated with the aid of narrow-band contrast interference color filters. The degree of suppression of the parasitic signal in the optical system is not less than 10. The apparatus permits determination of the nitrogen density all the way up to applied pressures of about 1000 Pa. The measured values of the vibrational temperature of nitrogen are in the 850-1000°K range.