Development of a Stark shift measurement technique using excited-state oxygen atoms to determine electron number density in shock heated O2/Ar above 10\u2009000 K

Abstract

We present measurements of electron number density, n e, in partially ionized gases containing electronically excited atomic oxygen, at nominal translational temperatures between 10\u2009100–11\u2009200 K. The measurements were based on the Stark shift of the O( P35 ) to O( D2,3,405 ) transition at 926 nm. The current work scanned the laser across the transition and utilized the Stark shift of the absorbance for robust determination of n e. The measurements were conducted in a shock-heated 1% O2/Ar mixture, with a measurement time resolution of 20 μs. A line-center shift of −0.06 cm−1 was observed within around 500 μs of the test time after the mixture was instantaneously heated to 11\u2009200 K by the reflected shock wave, which corresponded to an electron number density increase from 0 to 2 ×\u2009 1021 m−3 due to collisional ionization. The measurement method and resulting data may be of interest in future studies of high-temperature air flows.