Diagnosis of Solid Objects underwater Using Laser Induced Plasma Spectroscopy Technique

Abstract

Laser Induced Breakdown Spectroscopy (LIBS) or Laser Induced Plasma Spectroscopy (LIPS) was intensively studied in the last decade as a new analytical technique. This technique deals with the study of the spectral distribution ofline intensities and the line shapes, of the optical emission and allow for an acceptable spatial & temporal resolution of the detected spectra. It is increasingly seen as a viable analytical technique. It is a promising tool for the analysis of trace impurities in metals. In LIBS technique, a powerful laser pulse is focused on a surface, a tiny amount of material is vaporized and through further photon absorption, it is heated up until it ionize and expand from the sample surface as a plasma cloud. This laser induced plasma is a micro--source of light that can be analyzed spectrally and temporally resolved detection of characteristic emission by a spectrometer. This is the principle of laser - induced plasma spectroscopy (LIBS). The ability to determine the composition of a metal surface under water is a milestone and has several applications. Examples include in situ detection of archeological objects sank under seawater or marine mines. In this thesis, LIBS has been utilized to determine the elemental composition of metal samples by forming micro plasma on the surface of a five standard Zn-Al metal alloy targets, both in air and underwater. Two different Nd:YAG laser sources working at 1 064-nm are

synchronized for underwater measurements by a two-channel pulse generator and steered along the same path by using beam splitter (40/60 % atl 064nm) then focused into metal sample, immersed underwater surface, while for air measurements a single laser source was used. A pair of optical systems was used, the first one was used to focus the beam on target and the