Terahertz polariton propagation in patterned materials

Generation and control of pulsed terahertz-frequency radiation have received extensive attention, with applications in terahertz spectroscopy, imaging and ultrahigh-bandwidth electro-optic signal processing 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 . Terahertz ‘polaritonics’, in which terahertz lattice waves called phonon-polaritons are generated, manipulated and visualized with femtosecond optical pulses 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , offers prospects for an integrated solid-state platform for terahertz signal generation and guidance. Here, we extend terahertz polaritonics methods to patterned structures. We demonstrate femtosecond laser fabrication of polaritonic waveguide structures in lithium tantalate and lithium niobate crystals, and illustrate polariton focusing into, and propagation within, the fabricated waveguide structures. We also demonstrate a 90° turn within a structure consisting of two waveguides and a reflecting face, as well as a structure consisting of splitting and recombining elements that can be used as a terahertz Mach–Zehnder interferometer 25 . The structures permit integrated terahertz signal generation, propagation through waveguide-based devices, and readout within a single solid-state platform.