Boosting photoconductive large-area THz emitter via optical light confinement behind a highly refractive sapphire-fiber lens

Enhanced THz radiation through a thick plasmonic electrode grating photoconductive antenna with tight photocarrier confinement

We propose the design of a photoconductive antenna (PCA) emitter with a plasmonic grating featuring a very high plasmonic Au electrode with a thickness of 170 nm. As we show numerically, the increase in h significantly changes the electric field distribution, owing to the excitation of higher-order plasmon guided modes in the Au slit waveguides, leading to an additional increase in the emitted THz power. We develop the plasmonic grating geometry with respect to maximal transmission of the incident optical light, so as to expect the excitation of higher-order plasmon guided Au modes. The fabricated PCA can efficiently work with low-power laser excitation, demonstrating an overall THz power of 5.3 μW over an ∼4.0 THz bandwidth, corresponding to a conversion efficiency of 0.2%. We believe that our design can be used to meet the demands of modern THz spectroscopic and high-speed imaging applications.

Topological Insulator Films for Terahertz Photonics

We discuss experimental and theoretical studies of the generation of the third terahertz (THz) frequency harmonic in thin films of Bi₂Se₃ and Bi_2-xSb_xTe_3-ySe_y (BSTS) topological insulators (TIs) and the generation of THz radiation in photoconductive antennas based on the TI films. The experimental results, supported by the developed kinetic theory of third harmonic generation, show that the frequency conversion in TIs is highly efficient because of the linear energy spectrum of the surface carriers and fast energy dissipation. In particular, the dependence of the third harmonic field on the pump field remains cubic up to the pump fields of 100 kV/cm. The generation of THz radiation in TI-based antennas is obtained and described for the pump, with the energy of photons corresponding to the electron transitions to higher conduction bands. Our findings open up possibilities for advancing TI-based films into THz photonics as efficient THz wave generators and frequency converters.