September 29, 2010
Another paper came out today, well its my paper so I think I should write a little bit about it . The study focuses on plasma-particle interactions in laser-induced plasmas. In this study, we tried to understand the fundamentals of dissociation and diffusion process in laser-induced plasmas starting from as early as 250 ns after the plasma is formed. In this study we also estimated diffusion coeffcient of Hydrogen atom. I will write in detail later but as of now here is the abstract of the article:
Study of analyte dissociation and diffusion in laser-induced plasmas: implications for laser-induced breakdown spectroscopy
Prasoon K. Diwakar, Sebastian Groh, Kay Niemax and David W. Hahn
J. Anal. At. Spectrom., 2010, Advance Article
DOI: 10.1039/C0JA00063A, Paper
Plasma–particle interactions are explored through the introduction of single microdroplets into laser-induced plasmas. Both spectroscopic analysis and direct imaging of analyte atomic emission are used to provide insight into the various fundamental processes, namely desolvation, atomization, and atomic diffusion. By doping the 50 µm droplets with Lu, Mg or Ca, the analyte excitation temperature and the ion-to-neutral emission ratio are explored as a function of plasma residence time following breakdown. The data suggest a change in the local plasma conditions about the analyte atoms around 15–20 µs following breakdown, which may be interpreted as an overall transition from localized (i.e. perturbed) plasma conditions to the global (i.e. bulk) plasma conditions. A direct assessment of the hydrogen atomic diffusion coefficient following analyte desolvation reveals a value of 1.7 m2 s−1 in the first 250–500 ns. This value is in good overall agreement with a theoretical analysis and with an analytical treatment of a surface source of hydrogen atoms. In contrast, calcium emission is only observed beyond about 1 µs, with a diffusion coefficient at least an order of magnitude below the hydrogen value. The temporal H and Ca emission data suggest that water vaporizes first, leaving an ever increasing Ca analyte concentration until finally, with nearly all water desorbed, the Ca fraction is vaporized. Overall, the data support the conclusion that finite time-scales of heat and mass transfer play an important role in localized plasma perturbations in the vicinity of the analyte, which has important implications for the LIBS analyte signal.