A transmission-type triple grating spectrograph for improved laser scattering diagnostics of low-density plasmas used in chemical analysis
A transmission-type triple grating spectrograph for improved laser scattering diagnostics of low-density plasmas used in chemical analysis
复制标题
DOI：
10.1039/d0ja00193g
复制
发表时间：
2020-09
影响因子：
3.4
通讯作者：
K. Finch;A. Hernandez;Y. She;Songyue Shi;G. Gamez
中科院分区：
文献类型：
--
作者：
K. Finch;A. Hernandez;Y. She;Songyue Shi;G. Gamez
迄今为止，各种各样的等离子体几何形状和模式已被用于化学分析，然而，就潜在机制而言，还有很多有待了解。等离子体诊断已被使用多年来阐明这些机制，其中最强大的技术之一是激光散射方法。激光散射提供了关于高能粒子分布的信息，包括动能和密度，这可以在最小扰动的情况下为化学分析等离子体的基本过程提供极有价值的见解。由于在低密度等离子体（如分析化学应用中所见）中区分来自竞争散射体的信号对仪器要求极其严格，自由电子的汤姆逊散射（TS）是最难实现的。尽管如此，为满足这些严格要求而开发的仪器相对较少。在本文中，将介绍一种用于TS的具有高数值孔径（0.25）/对比度（在532±0.5nm处≤10⁻⁶）/杂散光抑制（在532±22 - 32nm处约为1.8×10⁻⁸）的透射型三级光栅光谱仪（TGS）的设计和特性。此外，在典型的光发射光谱（OES）条件下对辉光放电进行的原理验证测量表明，新仪器具有高光通量和低检测限（在约1eV Te时约为10⁹cm⁻³）。
A wide variety of plasma geometries and modalities have been utilized for chemical analysis to date, however, there is much left to be understood in terms of the underlying mechanisms. Plasma diagnostics have been used for many years to elucidate these mechanisms, with one of the most powerful techniques being laser scattering approaches. Laser scattering provides information about the energetic species distributions, in terms of kinetic energy and densities, which can provide invaluable insights into the fundamental processes of chemical analysis plasmas with minimal perturbation. Thomson scattering (TS) from free electrons is the most difficult to implement due to the extremely stringent instrumental requirements for discerning the signal from competing scatterers in low-density plasmas, such as those seen in analytical chemistry applications. Nonetheless, relatively few instruments have been developed to satisfy these stringent requirements. In this paper, the design and characterization of a transmission-type triple grating spectrograph (TGS), with high numerical aperture (0.25)/contrast (≤10−6 at 532 ± 0.5 nm)/stray light rejection (∼1.8 × 10−8 at 532 ± 22–32 nm) required for TS, will be presented. In addition, proof-of-principle measurements on glow discharges operated under typical optical emission spectroscopy (OES) conditions demonstrate the high light throughput and low limits-of-detection (∼109 cm−3 at ∼1 eV Te) afforded by the new instrument.