Towards Compact and Sensitive THz Detection by Plasmonic-Enhanced Electro-Optic Sampling

We report a sensitive surface plasmon-enhanced THz detector in a standard free space electro-optic sampling (EOS) detection scheme. The plasmonic bull"s-eye antenna enhances the THz field by collecting and confining the incoming THz beam within the sub-wavelength region and reradiates it in the transmission side with negligible beam divergence to satisfy efficient spatial overlap with a NIR gating beam inside a second order nonlinear crystal. The optimized design is achieved numerically and fabricated with the femtosecond laser direct writing method as a reliable and scalable technique. The broad spectral band detection observed from 1.4 THz to 3.1 THz with up to 3.1 times enhancement in sensitivity at the plasmonic resonance frequency. This device effectively measures THz signals affected by beam wandering or varying spot sizes, paving the way for compact, sensitive THz detectors for wireless communications.