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Influence of focusing intensity on optically pumped metastable rare gas based on laser-induced ionization

•There is a competition relationship between ASE channel and fluorescence channel from Ar 4p[1/2]1 level.•The metastable 4s[3/2]2 level lifetime at the first stage could be obtained by the ASE intensity decay curve.•The metastable 4s[3/2]2 level lifetime at the second stage could be obtained by the...

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Published in:Journal of quantitative spectroscopy & radiative transfer 2023-12, Vol.311, p.108776, Article 108776
Main Authors: Hu, Shu, Huang, Ke, Zhu, Feng, Li, Juntao, Gai, Baodong, Cai, Xianglong, Xu, Ming, Guo, Jingwei
Format: Article
Language:English
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Summary:•There is a competition relationship between ASE channel and fluorescence channel from Ar 4p[1/2]1 level.•The metastable 4s[3/2]2 level lifetime at the first stage could be obtained by the ASE intensity decay curve.•The metastable 4s[3/2]2 level lifetime at the second stage could be obtained by the fluorescence intensity decay curve.•The 912.3 nm ASE pulse width was affected by the lifetime of 4p[1/2]1 level, metastable Ar (4s[3/2]2) concentration, plasma expansion rate, gain length, etc. When traditional optically pumped metastable rare gas laser (OPRGL) operating in high power output, a potential issue may arise: electromagnetic interference (EMI) caused by large volume atmospheric pressure discharge. This EMI problem imposes limitations on the application of OPRGL. We propose a new idea of preparing metastable atoms by 532 nm laser-induced preionization, which has the potential to circumvent the EMI problem. An 811.5 nm laser was used to excite the metastable (4s[3/2]2) Ar atoms in Ar-He mixture, resulting in the generation of a prominent amplified spontaneous emission (ASE) signal at 912.3 nm (4p[1/2]1→4s[3/2]2). By investigating intensities of the 912.3 nm fluorescence and ASE as a function of the delay time between 811.5 nm and 532 nm lasers, the influence of the 532 nm laser's focusing intensity on the evolution of prepared metastable atomic concentration was unveiled, as well as the amplification mechanism of 912.3 nm signal. Furthermore, the competition mechanism between ASE and the fluorescence channels originating from the 4p[1/2]1 level was studied. Considering the influence of plasma expansion on metastable atomic concentration, as well as the influences of threshold, gain and gain length on ASE, at the “photoexcitation + radiation + collisional relaxation” stage, we obtained a reliable effective lifetime of the metastable 4s[3/2]2 level through analysis of the decay curve of the 912.3 nm ASE intensity. Similarly, in the “ion-electron recombination” stage, a reliable effective lifetime of the metastable 4s[3/2]2 level was obtained by analyzing the decay curve of the 912.3 nm fluorescence intensity. Additionally, the 912.3 nm ASE pulse width was influenced by various factors, including the effective lifetime of the 4p[1/2]1 level, the concentration of metastable Ar, the plasma expansion rate, and the gain length, etc. This work demonstrates that OPRGL based on laser-induced preionization offers a promising alternative for the future advancement
ISSN:0022-4073
1879-1352
DOI:10.1016/j.jqsrt.2023.108776