The role of photon self-absorption on the H (n = 2) density determination by means of VUV emission spectroscopy and TDLAS in low pressure plasmas
The role of photon self-absorption on the H (n = 2) density determination by means of VUV emission spectroscopy and TDLAS in low pressure plasmas
复制标题
光子自吸收对低压等离子体中 VUV 发射光谱和 TDLAS 测定 H (n = 2) 密度的作用
DOI：
10.1088/1361-6595/abc93d
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发表时间：
2020
影响因子：
3.8
通讯作者：
U. Fantz
中科院分区：
文献类型：
--
作者：
F. Merk;R. Friedl;S. Briefi;C. Fröhler-Bachus;U. Fantz
用真空紫外（VUV）发射光谱法测定实验室低压等离子体中H（n= 2）原子的莱曼-α谱线密度时，受到等离子体中发射光子自吸收的强烈影响，导致对H（n= 2）原子密度的低估。利用逃逸因子法对真空紫外发射光谱测量得到的密度进行了校正。即使在低压等离子体中，应用的校正也可以达到数量级。必须对发射粒子和吸收粒子的空间分布以及相应的谱线轮廓作出假设。因此，执行额外的测量，这提高了对所应用的校正程序的基准的要求。相比之下，Balmer-α线上的可调谐二极管激光吸收光谱（TDLAS）是对H（n= 2）密度的直接测量，因此适合作为基准。对于所考虑的ICP，通过TDLAS获得的H（n= 2）密度接近3× 10 15 m− 3，而未校正的VUV发射光谱给出的值在大约10 13 m− 3的范围内，这取决于压力和施加的RF功率。计算出的逃逸因子约为2-8× 10− 3。一个很好的协议与TDLAS观察通过应用它们的结果的真空紫外发射光谱。
The H (n= 2) atomic density determination by means of vacuum ultra-violet (VUV) emission spectroscopy of the Lyman-α line in laboratory low pressure plasmas is strongly affected by self-absorption of emitted photons inside the plasma leading to an underestimation of this density. A correction of the densities obtained from VUV emission spectroscopy measurements is performed by using the escape factor method. The corrections applied can reach orders of magnitude even in low pressure plasmas. Assumptions on the spatial distribution of emitting and absorbing particles as well as on the corresponding line profiles have to be made. Consequently, additional measurements are performed, which raises the requirement of a benchmark of the applied correction procedure. In contrast, tunable diode laser absorption spectroscopy (TDLAS) on the Balmer-α line is a direct measurement of the H (n= 2) density and is thus suitable for a benchmark. For the ICP under consideration, H (n= 2) densities obtained via TDLAS are near 3× 10 15 m− 3 whereas uncorrected VUV emission spectroscopy gives values in the range of roughly 10 13 m− 3 depending on pressure and applied RF power. The calculated escape factors are on the order of 2–8× 10− 3. An excellent agreement with TDLAS is observed by applying them to the results of the VUV emission spectroscopy.