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Diagnostics of CO concentration in gaseous mixtures at elevated pressures by resonance enhanced multi-photon ionization and microwave scattering
Journal of Applied Physics ( IF 2.7 ) Pub Date : 2020-10-14 , DOI: 10.1063/5.0024194
Animesh Sharma 1 , Erik L. Braun 2 , Adam R. Patel 1 , K. Arafat Rahman 3 , Mikhail N. Slipchenko 2 , Mikhail N. Shneider 4 , Alexey Shashurin 1
Affiliation  

In this work, a novel diagnostic technique for carbon monoxide (CO) number density measurements in a nitrogen buffer mixture at elevated pressures up to 5 bar was developed and tested. The technique utilizes 2 + 1 resonance enhanced multi-photon ionization (REMPI) of CO induced by a femtosecond laser pulse at 230.1 nm, followed by detection of the number of REMPI-induced electrons using the microwave scattering (MS) method (REMPI-MS technique). Dependences of the number of REMPI-generated electrons on CO number density and laser energy were measured and analyzed in conjunction with a four energy level model of the CO molecule. The number of REMPI-induced electrons scaled linearly with CO number density up to about 5 × 1018 cm−3 and was independent of the buffer gas pressure up to 5 bar. Higher CO number densities caused saturation onset associated with laser beam energy loss while travelling through the gaseous mixture due to two-photon absorption and photoionization. The number of REMPI-induced electrons was found to scale cubically with the laser pulse energy for the tested energy range of 8–20 μJ (intensity in the focal region about 7–18 GW/cm2), which is consistent with the operation regime where the number density of excited CO molecules increases throughout the laser pulse duration and does not saturate in time. The linear scaling region of the REMPI-MS signal can be used for a CO number density diagnostic after appropriate calibration of the system.

中文翻译:

通过共振增强多光子电离和微波散射诊断高压下气体混合物中的 CO 浓度

在这项工作中,开发并测试了一种用于在高达 5 bar 的高压下测量氮缓冲混合物中一氧化碳 (CO) 数密度的新型诊断技术。该技术利用由 230.1 nm 飞秒激光脉冲诱导的 CO 的 2 + 1 共振增强多光子电离 (REMPI),然后使用微波散射 (MS) 方法 (REMPI-MS) 检测 REMPI 诱导的电子数量技术)。结合 CO 分子的四能级模型,测量和分析了 REMPI 生成的电子数量对 CO 数密度和激光能量的依赖性。REMPI 诱导的电子数量与 CO 数密度成线性比例,最高可达约 5 × 1018 cm-3,并且与高达 5 bar 的缓冲气体压力无关。由于双光子吸收和光电离,在穿过气体混合物时,较高的 CO 数密度导致与激光束能量损失相关的饱和开始。发现 REMPI 诱导电子的数量与 8-20 μJ 测试能量范围内的激光脉冲能量成立方比例(焦点区域的强度约为 7-18 GW/cm2),这与操作制度一致,其中激发的 CO 分子的数量密度在整个激光脉冲持续时间内增加并且不会及时饱和。在适当校准系统后,REMPI-MS 信号的线性标度区域可用于 CO 数密度诊断。发现 REMPI 诱导电子的数量与 8-20 μJ 测试能量范围内的激光脉冲能量成立方比例(焦点区域的强度约为 7-18 GW/cm2),这与操作制度一致,其中激发的 CO 分子的数量密度在整个激光脉冲持续时间内增加并且不会及时饱和。在适当校准系统后,REMPI-MS 信号的线性标度区域可用于 CO 数密度诊断。发现 REMPI 诱导电子的数量与 8-20 μJ 测试能量范围内的激光脉冲能量成立方比例(焦点区域的强度约为 7-18 GW/cm2),这与操作制度一致,其中激发的 CO 分子的数量密度在整个激光脉冲持续时间内增加并且不会及时饱和。在适当校准系统后,REMPI-MS 信号的线性标度区域可用于 CO 数密度诊断。
更新日期:2020-10-14
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