A mid-infrared laser absorption sensing method has been developed to quantify gas properties (temperature, pressure, and species density) at MHz measurement rates, with application to annular rotating detonation rocket flows. Bias-tee circuitry is integrated with distributed feedback quantum cascade and interband cascade lasers in the $$4{-}5~\mu \hbox {m}$$ range enabling diplexed radio frequency (RF) wavelength modulation on the order of several MHz while yielding sufficient scan depth to capture multiple rovibrational transitions in the fundamental vibrational bands of $${\text {CO}}$$ and $${\text {CO}}_{2}$$ . Sub-microsecond spectrally-resolved $${\text {CO}}$$ absorption lineshapes provide for inference of temperature and species from a two-line area ratio and pressure from collision line-width. $${\text {CO}}_{2}$$ column density is inferred from peak-to-valley differential absorption at the bandhead near $$4.19~\mu \hbox {m}$$ . A field demonstration on a methane-oxygen rotating detonation rocket engine was performed utilizing an in situ single-ended retro-reflection optical configuration aligned at the exhaust plane. The target gas properties are temporally-resolved at up to 3 MHz across rotating detonations with up to 20 kHz cycle frequency.

中文翻译：

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MHz 激光吸收光谱通过双工 RF 调制测量旋转爆轰火箭流中的压力、温度和物质

已开发出一种中红外激光吸收传感方法，以 MHz 测量速率量化气体特性（温度、压力和物种密度），并应用于环形旋转爆轰火箭流。Bias-tee 电路与 $4{-}5~\mu\hbox {m}$$ 范围内的分布式反馈量子级联和带间级联激光器集成在一起，能够实现几 MHz 量级的双工射频 (RF) 波长调制，同时产生足够的扫描深度来捕获 $${\text {CO}}$$ 和 $${\text {CO}}_{2}$$ 的基本振动带中的多个振动跃迁。亚微秒光谱分辨的 $${\text {CO}}$$ 吸收线形提供了从两线面积比和碰撞线宽压力推断温度和物种。$${\text {CO}}_{2}$$ 列密度是从 $$4.19~\mu \hbox {m}$$ 附近带头处的峰谷差吸收推断出来的。利用与排气平面对齐的原位单端后向反射光学配置对甲烷-氧气旋转爆轰火箭发动机进行了现场演示。目标气体特性在高达 3 MHz 的旋转爆炸中以高达 20 kHz 的循环频率进行时间分辨。