engleski

Study of backscattered atoms within laser produced plasma plume

When an intense focused laser pulse hits a solid or liquid target, dense and hot plasma is produced. This early stage is followed by rapid expansion into the vacuum or background gas environment. Most of particles move out perpendicularly to the target surface but due to collisions within the plume itself or with the background gas certain number of atoms is reflected back to the target. The backward scattering of ablated species is usually experimentally observed indirectly through deposits on the target. The Monte Carlo simulations1 have shown that up to 20% of atoms could be back reflected, depending on the background pressure. Both forward moving and backscattering atoms depend on many laser ablation (LA) parameters, such as laser fluence, beam profiles, focusing conditions, target size and shape, etc. Optimization of back flux on any of such parameter could be important in various applications of laser produced plasmas. In the present work we employed cavity ringdown spectroscopy (CRDS) technique2 to measure the Fe atom ground state densities through measurements of spectral line shapes in the regions above and below the target. To demonstrate the method properly, care was taken to keep LA parameters fixed. Peculiar line shapes were observed depending on temporal and spatial observation parameters. These lines were then interpreted through modeling which takes into account angular distribution of atoms and their velocity distributions3, 4. [1] A. Marcu, C. Grigoriu, and K. Yatsui, Appl. Surf. Sci. 248, 466 (2005). [2] I. Labazan and S. Milošević, Phys. Rev. A 68, 032901 (2003). [3] N. Krstulović, N. Čutić, and S. Milošević, Spectrochim. Acta, Part B 64, 271 (2009). [4] N. Krstulović, N. Čutić, and S. Milošević, Spectrochim. Acta, Part B 63, 1233 (2008).

laser produced plasma; backscattering; CRDS

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