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26 June 2001 Nonthermal effects in femtosecond laser damage of transparent materials
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Proceedings Volume 4423, Nonresonant Laser-Matter Interaction (NLMI-10); (2001)
Event: Nonresonant Laser-Matter Interaction (NLMI-10), 2000, St. Petersburg, Russian Federation
There are considered non-thermal processes of femtosecond laser-induced damage of wide band-gap transparent materials. Dominating of thermal or non-thermal effects depends on radiation and material parameters among which pulse repetition rate, focal spot size and absorption play key role. Non-thermal mechanisms of damage and ablation can dominate at initiating stage and at low repetition rates. They are attributed to nonlinear electrodynamical processes such as higher harmonic generation of formation of shock electromagnetic waves. Considering interaction of shock electromagnetic wave with a particle in potential well, we derive expression for threshold of laser-induced ionization and delocalization. Thermal mechanisms can dominate at later stages of damage and ablation at repetition rates above 10 kHz. There are also discussed after-heating and non- equilibrium non-thermal processes taking place between initiating and thermal stages. There are considered several mechanisms of laser-induced ionization - multiphoton, tunneling, avalanche ionization, also ionization by higher harmonics and by shock-wave front. Estimations of ionization rates show that the latter two mechanisms can dominate at initiating stage of femtosecond damage and determine critically following ionization processes. Obtained results are compared with experimental data.
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Vitali E. Gruzdev and Anastasia S. Gruzdeva "Nonthermal effects in femtosecond laser damage of transparent materials", Proc. SPIE 4423, Nonresonant Laser-Matter Interaction (NLMI-10), (26 June 2001);

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