Background: Hydrogen (H) and Carbon (C) are major elements that occur in various materials,
including organic matter. The identification and analysis of C and H are necessary for several
fields. LIBS is an excellent method for such analysis because it is rapid, and can be conducted remotely.
The technique has been employed for the analysis of H in zircaloy metals. However, few
studies on the emission characteristics of H and C in various gases have been undertaken because of
the difficulty of identifying H and C using standard LIBS techniques. In this work, the emission
characteristics of H and C were studied using pulsed CO2 LIBS. H and C elements were obtained
from ethanol vapor. Various gas environments were employed, including Nitrogen (N2), Argon (Ar),
and Helium (He) gases, in order to study the stability of the laser-induced plasma, the plasma lifetime,
and the excitation mechanisms of H and C.
Methods: The LIBS system used in this work consisted of a pulsed TEA CO2 laser (Shibuya SQ
2000), pulse generator, and optical multichannel analyzer. In this work, the laser with a wavelength
of 10.6 µm, pulse duration of 200 ns, and pulse energy of 3 J, was used as the irradiation source. The
laser energy used was 1.5 J. The laser was irradiated, and focused, using a 200 mm zinc selenide
(ZnSe) lens, onto a metal surface in order to initiate and induce a luminous plasma. The sample used
in this study was ethanol vapor, obtained from ethanol (99.5%, Merck). For this purpose, 10 mL ethanol
was poured into a glass beaker, and this was placed into a closed chamber that could be evacuated
by ambient gases including N2, Ar, and He gases.
Results: Identification of H emission line has been successfully carried out using this present technique
demonstrated in various gases including N2, Ar, and He. From the results, it was observed that
in N2 gas, the Hα I 656.3 nm emission line was clearly expressed, with a wide, full-width halfmaximum,
and quite a low emission intensity.
Conclusion: The emission characteristics of H and C in laser-induced plasma, produced in various
ambient gases, including N2, Ar, and He, were studied. The emission spectra of Hα and Hβ were expressed
clearly, with high intensity and low background emission, in He, while they were broad and
had high background emissions in N2 and Ar. Based on the time-resolved emissions, the Hα emission
had a longer lifetime in Ar and He. It was assumed that the metastable atoms of Arand He were predominant
in the excitation process of H and C. The characteristics of the H and C emissions in various
gases are important in selecting a suitable ambient gas for the study of light atomic emission in
the medical field, which mostly deals with organic materials containing H, C, and oxygen.