Extraordinary single cycle terahertz transmission through ensembles of sub-wavelength size metal particles

We investigate on-axis terahertz transmission through random collections of sub-wavelength sized metallic particles. Despite both the inherent opacity of the metallic particles at terahertz frequencies and the absence of straightline photon trajectories through the samples, we observe significant, polarized terahertz transmission through dense metallic particle collections, which are five orders of magnitude thicker than the radiation skin depth. The effects of sample length, particle size, particle shape, and conductivity on the enhanced transmission are explored experimentally and numerically. Our findings show that the polarized terahertz transmission is mediated by coherent near-field coupling of surface electromagnetic waves across the ensemble.