Fiber-optic laser-induced breakdown spectroscopy of zirconium metal in air: Special features of the plasma produced by a long-pulse laser

• Published in: Spectrochimica acta. Part B: Atomic spectroscopy 2018-04, Vol.142, p.37-49
• Main Authors: Matsumoto, Ayumu, Ohba, Hironori, Toshimitsu, Masaaki, Akaoka, Katsuaki, Ruas, Alexandre, Sakka, Tetsuo, Wakaida, Ikuo
• Format: Article
• Language: English
• Subjects: Air; Analytical methods; Electric power; Electric power sources; Emission analysis; Emission spectra; Fiber lasers; Fiber optics; Fiber-optic LIBS; Fukushima Daiichi decommissioning; Heavy metals; Laser induced breakdown spectroscopy; Lasers; Long-pulse laser; Metals; Molecular chains; Near infrared radiation; Nuclear energy; Nuclear power plants; Nuclear reactors; Optical fibers; Performance enhancement; Plasma; R&D; Research & development; Spectra; Spectroscopy; Wavelength; Zirconium
• ISSN: 0584-8547; 1873-3565
• DOI: 10.1016/j.sab.2018.01.012

The decommissioning of the Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Plant is an essential issue in nuclear R&D. Fiber-optic laser-induced breakdown spectroscopy (Fiber-optic LIBS) could be used for in-situ elemental analysis of the inside of the damaged reactors. To improve the performances under difficult conditions, using a long-pulse laser can be an efficient alternative. In this work, the emission spectra of zirconium metal in air obtained for a normal-pulse laser (6ns) and a long-pulse laser (100 ns) (wavelength: 1064nm, pulse energy: 12.5mJ, spot diameter: 0.35mm) are compared to investigate the fundamental aspects of fiber-optic LIBS with the long-pulse laser. The spectral features are considerably different: when the long-pulse laser is used, the atomic and molecular emission is remarkably enhanced. The enhancement of the atomic emission at the near infrared (NIR) region would lead to the observation of emission lines with minimum overlapping. To understand the differences in the spectra induced respectively from the normal-pulse laser and the long-pulse laser, photodiode signals, time-resolved spectra, plasma parameters, emission from the ambient air, and emission regions are investigated, showing the particular characteristics of the plasma produced by the long-pulse laser. [Display omitted] •Long-pulse laser (100ns) is employed in a fiber-optic LIBS instrument.•Emission spectrum of zirconium metal is compared with a normal-pulse laser (6ns).•Atomic and molecular emission is remarkably enhanced by the long-pulse laser.•Unique characteristics of the long-pulse plasma are experimentally presented.