The carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film was found to depend on the incidence polarization of the photoexciting beam. The modulation efficiency of terahertz transmission due to transverse-magnetic (TM)-polarized excitation is distinctly higher than that due to transverse-electric (TE)-polarized excitation. Underlying this difference is the enhancement of carrier injection when the TM-polarized light is more transmitted through the surface of organic thin films than the TE-polarization light.
We present that the carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film depends
on the incidence angle of photoexciting beam. At higher incidence angles of photoexciting beam, the modulation
efficiency of terahertz transmission due to TM-polarized excitation is distinctly higher than one due to TE-polarized
excitation. We find that this phenomenon is due to the enhancement of carrier injection which is expected when the
incident light is more transmitted through the organic thin film.
We investigate the terahertz (THz) transmission characteristics of complex slot arrays with various order of rotation symmetry. Our experimental results reveal that an asterisk-shaped aperture with sixfold rotational symmetry is the most appropriate shape for realizing polarization-independent, highly efficient, and frequency-selective transmission of THz radiation. A systematic understanding of the THz transmission characteristics is useful for achieving versatile platforms and custom-designed metallic devices with specific electromagnetic responses.
We investigate subwavelength confinement of terahertz electromagnetic surface modes in a three-dimensional
region with coupled slot structures. Two-dimensional resonance focusing on a subwavelength slot converts to
three-dimensional subwavelength confinement, due to sharp edge confinement effect on asymmetric
plasmonic structure, at the center position of the slot structures which consists of two or more slots. We also
report on the polarization independent confinement of terahertz electromagnetic surface modes beyond
diffraction limit. The structure which consists of radially arranged subwavelength slots located at a same
center position shows the polarization-independent terahertz three-dimensional subwavelength confinement.
We theoretically and experimentally investigate the optical properties of a subwavelength hole in a thin metallic
film. The microscopic origin of the hole plasmon resonance is a collective state formed by propagating thin film
surface plasmons of wavelengths equal to integer fractions of the hole diameter. We show that the plasmon
resonance depend strongly on the polarization of the incident light. We also, using time-domain terahertz
spectroscopy, demonstrate the first experimental observation of the optical coupling between antibonding film
plasmon modes and perpendicularly polarized light to the film surface.
Terahertz transmission filters have been manufactured by perforating metal surface structures with various geometric shapes which all support near-unity transmission at specific frequencies determined by geometric shape, symmetry, polarization, and lattice constant. Our results show that the structures specifically designed by the shape resonance are extremely versatile, dependable, easy to control and easy to make the multifunctional filters.
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