Scalable optical-to-terahertz converter with a prism-coupled plane-parallel lithium niobate plate

A nonlinear optical converter of femtosecond laser pulses to terahertz radiation, which combines the tilted-pulse-front pumping and prism coupling techniques, is proposed and experimentally tested. In contrast to the conventional tilted-pulse-front scheme with a prism-shaped LiNbO₃ crystal, the converter consists of a plane-parallel LiNbO₃ plate sandwiched between two dielectric prisms. One prism is used to couple the pump beam into the LiNbO₃ plate, another prism couples the generated terahertz radiation out of the plate. The proposed scheme enables scaling to large-diameter LiNbO₃ wafers and large-aperture high-energy pump laser beams resulting in generation of strong terahertz fields. In a proof-of-principle experiment with a 1-mm thick, small size (1 × 2 cm²) LiNbO₃ plate pumped by a mJ-class laser, the conversion efficiency comparable to that of the conventional scheme (∼0.1%) was demonstrated.