KTP Optical Parametric Oscillator for Extended Duration High Repetition Rate NO Planar Laser Induced Fluorescence

Abstract

Non-intrusive, high repetition rate flow visualization is imperative in understanding the flow physics of high-speed, turbulent, and reacting flow environments. Planar laser induced fluorescence (PLIF) is a useful technique that allows visualization of a single species in a planar slice of a flow with high signal to noise ratio. This provides higher spatial resolution over chemiluminescence. PLIF above repetition rates of 50 kHz can be performed with a series of crystals and mirrors oriented in a cavity and sum frequency mixing to make up an optical parametric oscillator (OPO). Previous work has used beta barium borate (BBO) crystals pumped by a 355 nm laser to excite species such as OH, NO, CH, and krypton. This work utilizes potassium titanyl phosphate (KTP) non-linear crystals and coated cavity optics pumped by a 532 nm laser to generate deep UV to excite multiple combustion relates species such as NO, OH, NO v2, CO, O, and CH. The benefits include higher repetition rates, higher damage threshold of optics, longer burst durations, and lower build cost. The KTP OPO is applied to perform NO and OH PLIF in an optically accessible rotating detonation engine combustor. This allows the injected gas and detonation dynamic response to be visualized.