Efficient electro-optic sampling detection and generation of intense THz radiation via Cherenkov-type phase matching in a LiNbO3 crystal coupled to a Si prism

Efficient terahertz (THz) wave generation via Cherenkov-type phase matching were demonstrated with a thin lithium niobate (LiNbO₃, LN) crystal coupled to a Si prism structure (Si-LN). This design relies on wave-guiding effects for the optical pump and decreased THz absorption in the LN crystal to achieve intense THz wave emission. Results showed that the peak value of the THz emission from a 40-μm-thick LN crystal is 7 times stronger than that of a 0.5 mm-thick crystal. In addition, an effective THz electro-optic (EO) sampling scheme was experimentally demonstrated using the same Si-LN structure and Cherenkov-phase matching scheme. The detected broadband THz peak signal via Cherenkov phase-matched EO-sampling using an 800-nm femtosecond probe beam and a Si prism-coupled 0.5 mm-thick LN crystal was measured to be 2.5 times higher than by standard EO sampling using collinear phase matching in a 4 mm-thick ZnTe crystal. The Cherenkov phase matching technique can be achieved with any probe wavelength and hence has an advantage over the collinear phase matching method.