No abstract

No abstract

The extreme nonlinear terahertz response of initially unexcited intrinsic semiconductor nanostructures is studied theoretically by solving extended semiconductor Bloch equations numerically. The coupled dynamics of intraband acceleration and multiphoton interband transitions leads to high-harmonic generation up to several tens of the exciting terahertz frequency. It is shown that the actual cut-off frequency is determined by the band structure and not by the excitation strength. 1 Introduction Terahertz (THz) spectroscopy provides a powerful method to experimentally identify different quasi-particle states in optically excited semiconductors [1,2]. When the intra-excitonic 1s-to-2p transition is excited with a strong THz pulse, several different nonlinear and extreme nonlinear effects are observed [3,4] including Rabi flopping, generation of high THz harmonics, and the excitonic dynamical Franz-Keldysh effect.In this paper, we present calculations showing that very strong THz fields can even induce interband transitions via multi-photon processes. This establishes a new regime of THz physics that connects conventional THz excitations of semiconductors with the field of extreme nonlinear optics [5][6][7].We use our microscopic theory to compute the coherent light emission of an unexcited intrinsic semiconductor nanostructure in the presence of an extremely intense THz field. For strong enough excitation, we obtain high-harmonic generation (HHG) with frequency components within the far ultraviolet range. This HHG results from the coupled dynamics of the interband transitions and the classical intraband acceleration of the charge carriers. Since the THz field is highly off-resonant with respect to the interband transitions, peak field strengths of few MV/cm are required in order to excite a sufficient amount of carriers across the bandgap. Such strong fields have recently become available experimentally in the THz range [8,9].

No abstract

The anisotropic effective mass of energetic electrons in an isotropic, nonparabolic conduction band is revealed using ultrafast THz-pump-THz-probe techniques in a n-doped InGaAs semiconductor thin film. A microscopic theory is applied to identify the origin of the observed anisotropy and to show that the self-consistent light-matter coupling contributes significantly to the THz response.