Abstract
Optically controlled one-dimensional photonic crystal structures for the THz range are studied both theoretically and experimentally. A GaAs:Cr layer constitutes a defect in the photonic crystals studied; its photoexcitation by 800 nm optical femtosecond pulses leads to the modulation of the THz beam. Since the THz field can be localized in the photoexcited layer of the photonic crystal, the interaction between photocarriers and THz light is strengthened and yields an appreciable modulation of the THz output beam even for low optical pump fluences. Optimum resonant structures are found, constructed and experimentally studied. The dynamical response of these elements is shown to be controlled by the lifetime of THz photons in the resonator and by the free carrier lifetime. The time response of the structures studied is shorter than 330 ps.
Highlights
Generation, detection and control of pulsed and continuous-wave terahertz (THz) radiation have received considerable attention during last years
photonic crystal (PC) samples were characterized by time-domain THz spectroscopy using a standard transmission setup for steady-state measurements and an optical pump—THz probe setup [19] for
The generated THz pulses were focused onto the sample by an ellipsoidal mirror; the transmitted THz radiation was directed to the ZnTe sensor by using another ellipsoidal mirror
Summary
Generation, detection and control of pulsed and continuous-wave terahertz (THz) radiation have received considerable attention during last years. The THz properties of undoped semiconductors like Si or GaAs can be modified by optical pulses or cw radiation [5, 6, 7, 8, 9, 10] These materials are transparent for the THz radiation in their ground states whereas the inter-band photoexcitation leads to the generation of free mobile carriers which induce a dramatic increase of absorption in the THz range. [11] have taken advantage of ultrafast properties of ErAs/GaAs multilayers [12] and of a two-dimensional (2D) electrically resonant metamaterial structure with sub-wavelength pattern They have demonstrated THz switching capabilities of the structure at the photocarrier density level of 1016 cm−3 with a response time of about 20 ps. An ultrafast response of our devices is demonstrated by using the optical pump—THz probe experimental technique
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