Controlling anisotropy of dielectrics by an ultrashort double-pulse laser

We theoretically investigate the control of optical responses of dielectrics by an ultrashort double-pulse laser, based on the real-time time-dependent density functional theory. Taking the diamond as a concrete example, we demonstrate the unique capability of a purposely designed double-pulse laser in manipulating the strong anisotropy of dielectrics, achieving significant benefits compared with a single-pulse laser. With easily tunable laser parameters, the dielectric material can even be switched by reversal of isotropic, elliptic and hyperbolic for a particular light frequency at certain time points during the pulse laser. We describe the evolution of the transient permittivity throughout the duration of the pulse laser, which can exhibit reversible but deeply nonlinear modification in optical responses driven by a purposely designed pulse laser without imposing physical damage, demonstrating a fundamental possibility for applications of ultrafast all-optical signal processing and optical-field effect devices. (paper)