engleski

Background gas effects on laser produced plasma studied by cavity ring-down spectroscopy

Producing plasmas with energetic photons (lasers) in comparison to electrons (discharges) brings opportunity to obtain different plasma chemistry which then leads to various applications. Laser produced plasmas are used in many areas and particularly in materials research. In all applications detailed plasma diagnostics is needed to control plasma processes. The main diagnostic tool for pulsed laser produced plasma relies on the time gated spectroscopy of plasma emission. However emission spectroscopy gives no information about the dark content of the plasma, e.g. densities of ground state or metastable states within the plume, or about the backscattered atoms or molecules. In the present work we used spectroscopic absorption technique, cavity ring-down spectroscopy (CRDS) which offers spatially and temporally resolved measurements of the plume content with very high sensitivity [1]. Plasma was produced by a nanosecond Nd:YAG laser at 1064 nm with irradiance from 0.8 to 11×109 W/cm2. Measured absorption line shapes were compared to simulation based on the simple model developed in order describe specific effects of the laser produced plasma plume and CRDS technique. We have studied forward and backward moving atoms within the iron laser produced plasma plume at background helium gas pressures ranging from 10−5 to 1 mbar [2]. Changes of absorption line shapes were used to estimate kinetic parameters (the angular and velocity distributions of atoms in the expanding plume) of the iron plasma plume. The amount of backward scattered atoms was found to be about 10% of the total number of particles. In the presence of helium background gas, density of the 23S1 metastable helium has been measured depending on the laser ablation of various materials (graphite, aluminum, and iron) [3]. The highest yield of metastables was found in the case of aluminum target (0.05%). For metals, production rate is discussed in terms of work function and ionization potential. The above findings are discussed in terms of two applications, pulsed laser deposition of nanoparticles [4] and laser induced breakdown spectroscopy of metal alloys where strong increase of signal is observed in the presence of helium gas. The results shown are part of investigation performed within the project no. 035-0352851-2856 supported by the Ministry of Science, Education and Sport of the Republic of Croatia. References [1] S. Milošević, AIP Conference Proceedings 1438, (2012) 149-154 [2] M. Bišćan, S. Milošević, Spectrochimica Acta Part B: Atomic Spectroscopy, 68 (2012) 34-39. [3] M. Bišćan, S. Milošević, Spectrochimica Acta Part B: Atomic Spectroscopy 81 (2013) 20-25. [4] P. Dubček, B. Pivac, S. Milošević, N. Krstulović, Z. Kregar, S. Bernstorff, Applied Surface Science, 257, (2011) 5358-5361.

laser produced plasma; background gas effects

nije evidentirano