Response of semiconductors and fullerenes to ultrashort and ultra-intense laser pulses

We report new theoretical studies of the electronic and structural response of materials to fast intense laser pulses, with durations ∼ 10-100 femtoseconds and intensities up to ∼ 10 terawatts/cm². The results provide still stronger evidence that GaAs undergoes a true nonthermal phase transition as the intensity is varied at constant pulse duration. For C₆₀, there are also different regimes of behavior as a function of pulse intensity. At low intensity, various optically-active modes are observed. At high intensity, the breathing mode is by far the most dominant. At still higher intensities, there is photofragmentation, with the evolution of dimers and other products. These results were all obtained in simulations using tight-binding electron-ion dyanamics (TED).