Laser-Induced Desorption Spectroscopy with an Inductively Coupled Plasma Source—Examination of Technique Applicability for Detection of Retained Hydrogen

We report the implementation of a method for non-destructive remote diagnostics of the content of gas impurities retained in a material surface layer. The technique is based on the laser-induced heating of a surface layer and associated desorption of gas species in the presence of background inductively coupled plasma (ICP). The analysis of released gas species is made by optical emission spectroscopy (OES). The procedure of optimizing the signal efficiency by changing the spectrometer observation path with respect to the laser beam and the delay of spectrum acquisition is discussed. The applicability of laser-induced desorption spectroscopy (LIDS) was examined by studying the release of hydrogen from a Ti-V test sample exposed to Nd:glass laser pulses (λ = 1064 nm, duration 0.5 ms, energy 1–14 J), in a background argon plasma, by measuring the intensity of Balmer spectral lines. The demonstrated dependence of H_α intensity on the laser pulse energy enables implementing the LIDS technique for diagnostics of retained hydrogen. The lower limit of the laser pulse energy range suitable for diagnostics is associated with spectrometer sensitivity. The higher limit is governed by distortion of plasma conditions, which is detected as a deviation in argon emission intensity from constant value when the laser pulse energy exceeds 6 J.