Ultrafast opto-terahertz photonic crystal modulator

We present an agile optically controlled switch or modulator of terahertz (THz) radiation. The element is based on a one-dimensional photonic crystal with a $\mathrm{GaAs}$ wafer inserted in the middle as a defect layer. The THz electric field is enhanced in the photonic structure at the surfaces of the $\mathrm{GaAs}$ wafer. Excitation of the front $\mathrm{GaAs}$ surface by ultrashort $810\mathrm{nm}$ laser pulses then leads to an efficient modulation of the THz beam even at low photocarrier concentrations $(\approx {10}^{16}{\mathrm{cm}}^{-3})$. The response time of the element to pulsed photoexcitation is about $130\mathrm{ps}$.