The average effective mass of charge carriers produced by an intense ultrashort laser pulse in a transparent solid increases significantly as the excitation mechanism changes from multiphoton transitions to interband tunneling. We theoretically investigate this phenomenon for several dielectrics and semiconductors. For diamond as a representative dielectric, we present a detailed analysis of the laser-induced change of optical properties. When the concentration of free carriers is high, we find that the average effective mass controls not only the intraband charge-carrier transport but also the interband contributions to the optical response. We observe that the excitation-induced birefringence is particularly large for parameters where the plasma response compensates for the linear response of an unperturbed solid. arXiv:1804.09030v2 [cond-mat.mes-hall] 20 Nov 2018 * vladislav.yakovlev@mpq.mpg.de 1 H. M. van Driel, Appl. Phys. Lett. 44, 617 (1984).

Figure 4. a) EOS (in red) and b) LPS (in blue) spectral response functions calculated with different GDD values applied to the VIS-UV pulse. c) EOS response calculated for a compressed VIS-UV pulse and different crystal thicknesses.

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In this paper, a broadband multi-layered active metamaterial design is investigated, which can achieve a high polarization conversion efficiency over a wide band of frequencies in the terahertz regime. The design can be switched to an efficient metamaterial absorber using the phase transition property of vanadium dioxide (VO2). Additionally, the designed structure can convert the linear polarization of the incoming wavefronts to its cross-polarization and linear polarization to circular polarization in the reflection mode. The broadband characteristic is achieved due to the strong anisotropic behavior of the metasurface. The structure is robust to a wide range of incident angles as well. The proposed switchable multifunctional design can contribute to the development of active plasmonic polarization devices and metamaterial absorbers.