The physical mechanisms for damage formation in graphite films induced by femtosecond laser pulses are analyzed using a microscopic electronic theory. We describe the nonequilibrium dynamics of electrons and lattice by performing molecular dynamics simulations on time-dependent potential energy surfaces. We show that graphite has the unique property of exhibiting two distinct laser-induced structural instabilities. For high absorbed energies ( $>3.3\mathrm{eV}/\mathrm{atom}$) we find nonequilibrium melting followed by fast evaporation. For low intensities above the damage threshold ( $>2.0\mathrm{eV}/\mathrm{atom}$) ablation occurs via removal of intact graphite sheets.

• Received 29 November 2000

DOI:https://doi.org/10.1103/PhysRevLett.87.015003