Spatial evolution of nitric oxide in ns-discharges using a 250 kHz optical parametric oscillator

Abstract

In this article we present burst-mode nitric oxide laser-induced fluorescence (LIF) measurements at 250 kHz probing the first 500 µs evolution of a nanosecond repetitively pulsed discharge in the spark regime. The discharge energy was varied from 140 µJ to 180 µJ by adjusting the excitation voltage. The probe laser beam at 226 nm was produced by doubling the 452 nm output of an optical parametric oscillator (OPO) pumped by 355 nm output of a burst-mode laser. It was observed that the nitric oxide produced by the discharge developed a toroidal distribution around the electrode central axis over the first 200 µs after the last spark discharge with the maximum local nitric oxide concentration of 1.8 × 1024 m−3. The expansion of the toroidal distribution was tracked over time and space by the pulse-burst laser pumped OPO system for the first time.