Ablazione Laser di Metalli con Impulsi Ultracorti - Ultrashort Laser Ablation of Metals

The project is in the field of interaction of ultrashort laser pulses with metals. The rapid development of short-pulsed laser systems over the last years offered opportunities for high-precision material processing and structuring of a wide range of materials – metals,1-3 semiconductors,4 and organic solids.5 Besides a variety of practical applications of ultrashort laser pulses they also reveal some new fundamental aspects of laser-beam interactions with matter. Laser ablation is a basic mechanism in a large number of applications for laser processing: cutting, drilling, surface cleaning, pulsed laser deposition of thin films, etc. Recent investigations showed that its theory and modeling are very complex. The process depends strongly on the material’s properties and the parameters of the laser source. Moreover, its theory requires the combination of several different areas of physics. This is why the fundamental physics underlying the laser ablation mechanism is still unclear. Additionally, the description is complicated in the case of ultrashort-pulse laser ablation because of the number of non-thermal processes involved. Many theoretical models have been developed recently,6-8 based generally on the heat conduction equation, hydrodynamics and molecular dynamics, which try to bring to light the basic features of short-pulse laser ablation process. According to these studies, several mechanisms of the ablation process can be realized, depending on the material and laser parameters. Some authors describe the ablation as melting followed by vaporization. Others indicate that a critical pressure gradient, arising in the short time interval after the laser interaction, is in the origin of the ejection process. In this case, the energy is deposited faster than the time of acoustic wave formation in the system, and the relaxation of the pressure gradient created leads to a significant material removal. On the other hand, if the laser pulse duration is shorter than the time for thermal relaxation of the system, defined by the thermal diffusion, overheating of the system can take place. Then, the temperature in the material reaches the critical point and a fast transition to a gaseous-liquid phase (phase explosion) occurs. Experimentally, basic properties and dynamics of ultrashort laser ablation have not yet been established, and experiments that focus on the ablated species are still rare. A few studies recently published have limited themselves to establish the presence of different species in the ablated plasma plume, namely ions, neutral atoms and nanoparticles.9-11 In the present context the formation of: i) nanoparticles with a diameter in the  1-10 nm range; ii) sub-keV to keV ions, during ultrashort laser ablation of solid targets, constitute aspects on great interest, due to their possible applications. In fact, the former (i) could open up new route to the production of nanoparticles resulting of special interest in the field of nanophysics and nanotechnology, while the latter (ii) is considered particularly promising for the current deficiency of sub-keV high-flux ion beams delivered by presently available commercial techniques. The main goals of the project are concentrated on: • development of a reliable numerical method based on Molecular dynamics simulation technique describing interaction of the ultrashort (<10 ps) laser radiation with metals; • detailed investigation of the process of ultrashort laser ablation of metals, including mechanisms of ablation, processes involved in the target material – phase transitions, shock wave evolution, crater formation, structure and evolution of the ablated material; • detailed experimental investigations of the characteristics of laser ablation driven by ultrashort laser pulses through the analysis of the ejected material, as well as on their variation as a function of the laser pulse characteristics (energy density, wavelength, e.g.). The result obtained in the frame of the project can be used in different areas of application of ultrashort lasers – precise micromachining, pulsed laser deposition of thin films, nanoparticles generation, etc., as well as they can reveals the physical nature of the processes involved. References: 1 S. Preuss, A. Demchuk, and M. Stuke, Appl. Phys. A 61, 33 (1995). 2 S. Nolte, C. Momma, H. Jacobs, A. Tünnermann, B.N. Chichkov, B. Wellegehausen, and H. Welling, J. Opt. Soc. B 14, 2716 (1997). 3 P.S. Banks, M.D. Feit, A.M. Rubenchik, B.C. Stuart, and M.D. Perry, Appl. Phys. A 69, 377 (1999) 4 D. von der Linde and K. Sokolowski-Tinten, Appl. Surf. Sci., 154, 1 (2000). 5 L.V. Zhigilei, P.B.S. Kodali, and B.J. Garrison, J. Phys. Chem. B 102, 2845 (1998). 6 A.M. Stonehman, M.M.D. Ramos, R.M. Ribeiro, Appl. Phys. A 69, S81 (1999) 7 L.V. Zhigilei, Appl. Phys. A 76, 339 (2003). 8 A.M. Rubenchik, M.D. Feit, M.D. Perry, J.T. Larsen, Appl. Surf. Sci., 127-129, 193 (1999). 9 O. Albert, S. Roger, Y. Glinec, J.C. Loulergue, J. Etcheparre, C. Boulme-Leborgne, J. Perriere, E. Millon, Appl. Phys. A 76, 319 (2003). 10 S. Amoruso, X. Wang, C. Altucci, C. de Lisio, M. Armenante, R. Bruzzese, N. Spinelli, R.Velotta, Appl. Surf. Sci. 186, 358 (2002). 11 M. Spyridaki, E. Koudoumas, P. Tzanetakis, C. Fotakis, R. Stojan, A. Rosenfeld, I.V. Hertel, Appl. Phys. Lett. 83, 1471 (2003). Our publications in the field: 1. N.N. Nedialkov, S.E. Imamova, P.A. Atanasov, G. Heusel, D. Breitling, A. Ruf, H. Hügel, F. Dausinger, P. Berger, Appl. Surf. Sci. accepted for publication (2003). 2. S. Amoruso, X. Wang, C. Altucci, C. de Lisio, M. Armenante, R. Bruzzese, N. Spinelli, R.Velotta, Appl. Surf. Sci. 186, 358 (2002). 3. P. Atanasov, N. Nedialkov, S. Imamova, A. Ruf, H. Hügel, F. Dausinger, P.Berger, Appl. Surf. Sci., 186, 369 (2002). 4. M. Obara, P.A. Atanasov, Y. Hirayama, K. Ozono, N.N. Nedialkov, S.E. Imamova, Proc. APLS’02, 1 (2002). 5. P. Atanasov, N. Nedialkov, S. Imamova, H. Hügel, F. Dausinger, A. Ruf, Proc. SPIE, 4397, 290 (2001). 6. S. Amoruso, Appl. Phys. A 69, 323 (1999). 7. S. Amoruso, R. Bruzzese, N. Spinelli, R.Velotta, J. Phys. B 32, R131 (1999).