Characteristics of coherent forward scattering spectrometry in Faraday configuration measured with a diode laser on the 842.5 nm Ar I and 844.6 nm O I lines

Abstract

In this study, a coherent forward scattering (CFS) spectrometer with permanent magnets in the Faraday configuration was developed. Neodymium ring magnets (Nd–Fe–B) were used to apply an external magnetic field to a radio frequency (RF) glow discharge. The effect of using a single or double magnet configuration on the transmitted CFS intensity was investigated. The resulting analytical curve of the CFS signal intensity on the Ar I 842.46nm line rises with the 3.34±0.17-th power of the argon partial pressure, which is larger than the theoretically expected quadratic slope. In addition, an 844.6nm atomic oxygen line (33P–33S) is investigated as an example of a weak absorption transition from the short-lived lower level (lifetime=1.74ns). Despite the population inversion and the short-lived lower level, the absorption transition of O I 844.6nm could be detected, and analytical curves in noble gas–O2 RF glow discharges were recorded successfully. The CFS signal intensities rose with the 1.65±0.24-th power of the partial pressure of O2 in neon, with the 1.95±0.05-th power in argon, and with the 2.15±0.23-th power in helium. The estimated values are close to the theoretically expected quadratic dependence.