Development of a Stark shift measurement technique using excited-state oxygen atoms to determine electron number density in shock heated O2/Ar above 10 000 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 10 100–11 200 K. The measurements were based on the Stark shift of the O( P 3 5 ) to O( D 2 , 3 , 4 0 5 ) 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% O 2 /Ar mixture, with a measurement time resolution of 20 μ s. A line-center shift of −0.06 cm −1 was observed within around 500 μ s of the test time after the mixture was instantaneously heated to 11 200 K by the reflected shock wave, which corresponded to an electron number density increase from 0 to 2 × 10 21 m −3 due to collisional ionization. The measurement method and resulting data may be of interest in future studies of high-temperature air flows.