The coupling effects of surface plasmon resonance (SPR) from metamaterials induce variation in both the frequency and intensity of plasmonic modes. Here, we report an angular-dependent THz modulator with hybrid metal–graphene metastructures. The metastructures composed of the period gold split-rod arrays on top of a monolayer graphene, which show redshift modulation in the THz region with an increasing incident angle due to the strong out-of-plane magnetic flux introduced by the clockwise circular current at the oblique incidence. By utilizing graphene-based actively tunable conductor with ion-gel electrical gating, the THz transmission can be significantly modified. The modulation depth of the hybrid metal–graphene metastructure modulator can reach ~37.6% at 0.62 THz with a gate voltage of −3 V. The theoretical modeling of transmitted dependency on frequency and incident angle is demonstrated at different Fermi energies, which fits well with the experimental results. This hybrid device can offer a useful method for THz applications (such as angle sensors or angular-resolved spectroscopy), where angle-dependent modulation is needed.

Benefiting from a high quantum efficiency, low thermal emittance, and large absorption coefficient, In_xGa_1−xAs is an excellent group III–V compound for negative electron affinity (NEA) photocathodes. As the emission layer, In_xGa_1−xAs, where x = 0.15, has the optimal performance for detection in the near-infrared (NIR) region. Herein, an NEA In_0.15Ga_0.85As photocathode with Al_0.63Ga_0.37As as the buffer layer is designed in the form of a transmission mode module. The electronic band structures and optical properties of In_0.15Ga_0.85As and Al_0.63Ga_0.37As are calculated based on density functional theory. The time response characteristics of the In_0.15Ga_0.85As photocathode have been fully investigated by changing the photoelectron diffusion coefficient, the interface recombination velocity, and the thickness of the emission layer. Our results demonstrate that the response time of the In_0.15Ga_0.85As photocathode can be reduced to 6.1 ps with an incident wavelength of 1064 nm. The quantum efficiency of the In_0.15Ga_0.85As photocathode is simulated by taking into account multilayer optical thin film theory. The results indicate that a high quantum efficiency can be obtained by parameter optimization of the emission layer. This paper provides significant theoretical support for the applications of semiconductor photocathodes in the near-infrared region, especially for the study of ultrafast responses in the photoemission process.