Monte Carlo calculations of laser-induced free-electron heating in SiO2

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Abstract
Free electron heating in SiO2 in the presence of high intensity laser excitation at 1 micron wavelength was investigated. The formalism is based on a Monte Carlo integration of the Boltzmann transport equation which has successfully explained dc transport data. The simulations were based on experimentally determined electron-hole pair excitation rates and energy dependent electron-photon scattering rates. Average power loss of conducting electrons to the lattice via phonon excitations increases rapidly with incident laser power. This allows for strong free carrier induced lattice heating and melting well below the onset of carrier multiplication by impact ionization. Chance momentum reversal in phase with the oscillating electric field results in a long high energy tail in the electron energy distribution. For high laser intensities this high energy tail will lead to strong carrier multiplication. High temperatures may suppress carrier multiplication. Free carrier heating, single shot laser breakdown, and avalanche induced prebreakdown lattice heating are discussed. A new mechanism for single shot prebreakdown laser heating which combines impact ionization and free electron heating is proposed.

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