Abstract
Angular dependence of extraordinary terahertz (THz)-wave transmission is investigated in a bull’s eye
structure : a subwavelength aperture with concentric grooves. Split resonant peaks in transmission
spectra are observed using high-resolution THz spectroscopy with an injection-seeded THz-wave
parametric generator used as a bright, tunable THz-wave source. The resonant frequency at normal
incidence agrees well with finite-difference time-domain calculation. With the incident angle varied
from 0-5 deg, the resonant frequencies are tuned in the frequency range of 180 GHz with the rate of 18
GHz/deg. The behavior is well explained by the folded dispersion curve of surface plasmons at THz
frequencies. The measured Q values are 27 at normal incidence, 11 and 14 at 5 deg.
