Rayleigh scattering as a nonintrusive diagnostic for electric-field strength

Abstract

Rayleigh scattering has been investigated in an effort to develop a nonintrusive diagnostic for electric-field strength at moderate (~1 atm) to high pressures. Both experimental and theoretical studies have been made, with experiments conducted on He, Ar, N2, CO2 C4, Kr, and air, and with theory confined to He. In all cases, the Rayleigh signal decreased with increasing applied field strength. However, no depolarization due to the applied field was found. Thus, although the effect appears to be applicable to any gas, there is no obvious means of separating electric-field effects from changes in the gas density. The measurement is most sensitive in a right-angle scattering configuration. At field strengths of 60 kV/cm, ~1 J of light energy is required to make a measurement. The largest effect was seen in neon, in which the electric field-induced differential cross section is 4 × 10−32 cm2/(kV)2 sr; the cross section for air is 3.5 × 10−32 cm2/(kV)2 sr. Calculations of the effect have been made using quantum perturbation theory and extended tables based on the Coulomb approximation. These calculations agree with the general behavior of the experimental results and give oscillator strengths for Stark-induced forbidden transitions as well.