Electro-Optic Sampling of Terahertz Pulses by using GaAs and Tapered Parallel Plate Waveguide

We demonstrate experimentally highly sensitive electro-optic sampling of THz pulses by $1.55-\mu\mathrm{m}$ -wavelength femtosecond laser pulses in a 0.1-mm thick and 10-mm long GaAs crystal inserted into a tapered parallel plate waveguide. High sensitivity is achieved due to THz field focusing by the waveguide and noncollinear velocity matching of the optical and THz pulses in the crystal. More than 20 times more efficient detection than in a 1-mm thick ZnTe crystal at $1.55\ \mu\mathrm{m}$ has been obtained.