Measurement of vibrational populations in low-pressure hydrogen plasma by coherent anti-Stokes Raman scattering

Abstract

Coherent anti-Stokes Raman scattering (CARS) has been applied to the measurement of vibrational populations in a low-pressure H2 plasma. We describe the plasma generator and give some particulars of the optical arrangement. For an electron density of 2×1011 cm−3 and a total pressure of 0.13 mbar, the rotational temperature is found to be 475 K. The populations of vibrational states v = 0, 1, and 2 have also been measured. Their distribution is non-Boltzmann. The influence of pressure and discharge parameters is briefly discussed. The instrument detection sensitivity for a given rovibrational state is about 1012 cm−3.