Manipulation of the dielectric properties of narrow-band gap material by an ultrashort laser pulse

The control of dielectric responses of narrow-band gap materials by an ultrashort laser pulse is investigated theoretically using time-dependent density functional theory, taking gallium phosphide as a concrete example. We demonstrate that, by using properly selected laser parameters an ultrashort laser pulse can induce reversible change of the electric and optical properties. The anisotropy of the transient permittivity of the material throughout the pulse duration can be enhanced so strongly that the dispersion of electromagnetic waves in the material becomes hyperbolic in some frequency interval with increasing laser energy. We describe the evolution of the transient permittivity throughout the duration of the laser pulse, pointing out to a fundamental possibility for applications of ultrafast all-optical signal processing and optical-field effect devices.