Terahertz Radiation from Semiconductors
We provide a review of the different schemes for generating terahertz (THz) radiation using photoconductive emitters excited by femtosecond lasers. The discussion is concerned principally with large-area emitters because of their relative simplicity, both in fabrication and analysis, and their capabilities for high-power THz generation. In addition to discussing the principal characteristics of these emitters, we present a simple, but unified description of their behavior. The principal ingredients in this description are a Drude--Lorentz model for the carrier dynamics combined with a suitable solution of the radiation problem for a current sheet. This formalism permits one to examine the nature of the generated THz waveforms in the near and far field, as well as to consider the effect of the material properties and excitation conditions on the THz emission process. Within this picture, we describe the origin of the strong enhancement in THz emission that is observed upon application of an external magnetic field to emitters relying on transient photocurrents flowing perpendicular to the surface. Saturation processes that limit the efficiency of THz emission are also an important feature of these devices. These effects are discussed in terms of perturbation of the bias field induced by space-charge screening and the THz radiation field.
Unable to display preview. Download preview PDF.