Active optical control of reflectivity in the terahertz range

The paper is about the all-optical devices allowing transfer of information from the optical spectral band to the THz one: opto-THz switches, modulators and phase-shifters. The experiments were performed on a semi-insulating GaAs sample using an optical pump-THz probe scheme. The amplitude of the THz wave reflected on the structure under investigation is closely related to the phase change. The wave exhibits a /spl pi//2-shift upon reflection under antireflecting conditions and a change of the sign (/spl pi/-shift) in high-reflectivity regime. The proposed structure acts as an optically controlled THz switch or as a phase shifter.