Contributions of Sub Target and Confinement Effects in Extension of Laser Induced Shock Wave Plasma Spectroscopy to Non-Metallic Targets
This is Doctoral Theses of R. Hedwig.
An experimental study has been carried out for the study and extension of laser induced shock wave plasma spectroscopy (LISPS) application to non metallic samples. For this purpose, a series of experiments were conducted to investigate the dynamical process taking place in the laser plasma generated by a high power and short pulse laser irradiations on a non metal samples. It was found that in the case of soft target, that the ablated atoms failed to induce a visible plasma at the surface of the target. With the support of a sub target however, it became possible, after a few laser shots depending on the target layer thickness, to generate the shock wave plasma emitting the characteristic spectral lines of the target material.
Another related phenomenon studied in this experiment is the pre-irradiation effect observed on a non metal hard sample such as quartz sample, which was characterized by the absence of secondary plasma at the initial shots. The disappearance of this effect at a later stage was found to be connected with the appearance of a crater of appropriate depth on the sample surface created by initial repeated irradiations on the sample surface. The plasma produced thereafter exhibited typical features of a secondary plasma. Further experiment employing artificial ring crater on the sample surface has eliminated the pre-irradiation effect completely, and has thus demonstrated that it is the confinement effect of the crater which was solely responsible for the generation of secondary plasma from the non metal hard target. This conclusion is in conformation with the shock wave model proposed earlier.
These experimental studies have thus considerably substantiated our understanding of the process of secondary plasma generation. In turn, this result helps to improve the quality and extend the scope of LISPS applications in the future.
laser-induced shock wave plasma, soft sample, sub target effect, spectrochemical analysis, confinement effect