Time evolution of second order susceptibility in GaAs following a fast intense laser pulse

Using the technique of tight-binding electron-ion dynamics, we have calculated the evolution of the non-linear susceptibility χ⁽²⁾(ω) in GaAs during the first few hundred femtoseconds following an ultrafast and ultra-intense laser pulse. Above a threshold fluence, our simulations show that χ⁽²⁾(ω) drops to zero, in agreement with the experimental measurements. The results indicate a rapid non-thermal transition from the original tetrahedral structure to a disordered structure, and support the conclusion that structural changes following ultrashort pulses are a direct consequence of bond destabilization.