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16 August 2000 Thermal and nonthermal effects in femtosecond laser ablation and damage of transparent materials
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Proceedings Volume 4065, High-Power Laser Ablation III; (2000)
Event: High-Power Laser Ablation, 2000, Santa Fe, NM, United States
There are considered non-thermal and thermal processes of femtosecond laser-induced damage and ablation of wide band-gap transparent materials. Dominating of one or other of them 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 (below 10 kHz). They are attributed to nonlinear electrodynamical processes such as higher harmonic generation and formation of shock electromagnetic waves. Considering interaction of shock electromagnetic wave with a particle (single charged particle and a dipole) placed 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. It is considered possibility of their description within modified two-temperature model. 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 of them can dominate at the stage of initiating of femtosecond damage and ablation and determine critically following ionization processes. Obtained results are compared with experimental data.
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Vitali E. Grudzev and Anastasia S. Gruzdeva "Thermal and nonthermal effects in femtosecond laser ablation and damage of transparent materials", Proc. SPIE 4065, High-Power Laser Ablation III, (16 August 2000);

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