Measurements of N2 refractive index and scalar polarizability in a pulsed nanosecond non-equilibrium discharge by Mach–Zehnder interferometry and spontaneous Raman scattering

Abstract

This paper presents quantitative measurements of the N2 Gladstone–Dale constant and scalar polarizability in non-equilibrium conditions, created by a nanosecond pulsed discharge at a pressure of 90 Torr. Optical path differences and spatially varying refractive index profiles are obtained by temporally-resolved Mach–Zehnder interferometry. Spontaneous Raman scattering spectroscopy is used to investigate the highly non-equilibrium vibrational population and to measure the N2() vibrational temperature and rotational temperature in the discharge afterglow region. The local gas density is inferred from the rotational temperature with isobaric conditions at long time delays ranging from 10 to 500 µs after initiating the pulsed discharge. The non-equilibrium effects on the N2 Gladstone–Dale constant and scalar polarizability are reported within a rotational temperature ranging from 300 to 1000 K. To the best of our knowledge, this is the first time the refractivity of gas has been measured under non-equilibrium conditions in a pulsed discharge afterglow.