Highly sensitive electro-optic detection of terahertz waves in a prism-coupled thin LiNbO₃ layer

Electro-optic sampling of pulsed terahertz radiation by femtosecond laser pulses in noncollinear geometry in a 40 μm thick layer of LiNbO₃ attached to a Si prism is experimentally demonstrated. Terahertz radiation is prism-coupled into the layer through its surface and modulates the frequency and angular spectra of the optical radiation propagating along the layer as a fundamental mode of a dielectric slab waveguide. The modulation results in the optical intensity variations in the optical beam transmitted through the layer. By measuring the intensity variations, we achieved 38 and 216 times enhancement in the sensitivity of electro-optic detection as compared to the conventional collinear ellipsometric technique with 1 mm thick ZnTe and 0.2 mm thick GaP crystals, respectively. (letter)