Improved method for measuring absolute O 2 (a 1 Δ g ) concentration by O 2 (a 1 Δ g → X 3 Σ g − ) IR radiation

• Published in: Review of scientific instruments 2004-11, Vol.75 (11), p.4455-4461
• Main Authors: Deng, Liezheng, Shi, Wenbo, Yang, Heping, Sha, Guohe, Zhang, Cunhao
• Format: Article
• Language: English
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.1793871

We describe an improved technique for measuring the absolute O 2 (a 1 Δ) concentration via the quantitative determination of IR radiation from O 2 (a 1 Δ g → X 3 Σ g − ) transition. An exact geometrical optical model was first established, in which the influence of reflection and refraction on the radiation characteristics of a luminous volume source was given full consideration, making possible the accurate calculation of the coupling efficiency between the volume source and a receiving area. Then, an IR radiation receiving apparatus (IRRRA) was constructed and its responsivity ( mV / W ) to the power of IR radiation calibrated by a tungsten standard lamp. An optical detection system was, in turn, built according to the optical model with fine alignment between the IRRRA and an optical cell. We then demonstrate the procedure to obtain the absolute concentration of O 2 (a 1 Δ) flowing through the optical cell from a jet singlet oxygen generator from the signal of the IRRRA, the optical cell volume, and the coupling efficiency between the cell and the IRRRA. Moreover, to verify the accuracy of this method, the absolute O 2 (a 1 Δ) concentration was compared to that measured by an established isothermal calorimetry method. Based on the comparison of the O 2 (a 1 Δ) concentrations determined by the two methods, the Einstein A -coefficient was estimated as (2.70±0.84)×10 −4   s −1 , which agrees with Badger’s value of 2.58×10 −4 , Špalek’s of 2.24×10 −4 , Newman’s of 2.19×10 −4 , and Miller’s of 2.3×10 −4 within the uncertainty of the experimental techniques. The method advanced in this article is worthwhile for the measurement of absolute O 2 (a 1 Δ) concentration in a chemical oxygen iodine laser or a singlet oxygen generator. It can also provide a general technique for the measurement of absolute concentrations of long-lifetime luminous species other than O 2 (a 1 Δ) .