Damage and ablation thresholds of fused-silica in femtosecond regime

Abstract

We present an experimental and numerical study of the damage and ablation thresholds at the surface of a dielectric material, e.g., fused silica, using short pulses ranging from 7 to 300 fs. The relevant numerical criteria of damage and ablation thresholds are proposed consistently with experimental observations of the laser irradiated zone. These criteria are based on lattice thermal melting and electronic cohesion temperature, respectively. The importance of the three major absorption channels (multi-photon absorption, tunnel effect, and impact ionization) is investigated as a function of pulse duration (7-300 fs). Although the relative importance of the impact ionization process increases with the pulse duration, our results show that it plays a role even at short pulse duration (<50 fs). For few optical cycle pulses (7 fs), it is also shown that both damage and ablation fluence thresholds tend to coincide due to the sharp increase of the free electron density. This electron-driven ablation regime is of primary interest for thermal-free laser-matter interaction and therefore for the development of high quality micromachining processes.

Transport and optical properties of warm dense aluminum in the two-temperature regime: Ab initio calculation and semiempirical approximation

“…Though the LeeMore model allows different temperatures of electrons and ions, only equilibrium curves T e = T i are available in the paper 18 . The Lee-More results are available for the density 2.5 g/cm 3 . We did not perform calculation for that particular density, but our data for the surrounding densities 2.…”

“…This discrepancy is most probably due to the used technical parameters (discussed in our previous work 39 ). The approach of Inogamov and Petrov also neglects the difference connected with the change of density from 2.35 g/cm 3 to 2.70 g/cm 3 . This change of the density increases thermal conductivity approximately by a factor 1.2 39 .…”

“…The experiments on the interaction of femtosecond lasers with matter are widespread nowadays [1][2][3][4] . During the ultrafast heating the matter passes through the twotemperature state with hot electrons and relatively cold ions.…”

Theory of dielectric nanofilms in strong ultrafast optical fields

“…For such pulses, the electron dynamics in the timedependent field of the pulse be described in terms of the density matrix whose evolution is determined by rate equations with phenomenological relaxation and generation times [19][20][21][22][23] . In this description, the effect of the pulse electric field is restricted to generation of an electronhole plasma through multiphoton or collisional ionization processes.…”

Determination of scattering properties and damage thresholds in tissue using ultrafast laser ablation

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