A technique enabling the generation of THz radiation using an ordered array of double-walled carbon nanotubes (DWCNTs) pumped by a direct electric current is proposed. The initial excitation of surface plasmon polaritons (SPPs) in the DWCNTs is performed by two laser beams with slightly different frequencies. The amplification of exited slow SPPs (with a phase velocity down to ~106 m/s) is provided by a drift current flowing through the DWCNTs. The DWCNTs with SPPs act as sources of THz radiation and emit coherent electromagnetic waves into free space. The proposed model of a carbon nanotube generator may be useful for the development of compact sources of coherent THz radiation.
The amplification and phase modulation of a surface electromagnetic wave propagating along a helical trajectory in a cylindrical semiconductor waveguide under the condition of phase matching with a longitudinal space-charge wave are considered. The evolution of a phase-modulated wave after passing through a semiconductor waveguide is studied and the conditions leading to the transformation of an initially stationary wave into a sequence of optical pulses with a terahertz repetition rate are determined.
A carbon nanotube (CNT) can be considered as a plasmonic waveguide enabling propagation of ultraslow (with the effective refractive index >100) surface electromagnetic waves in the THz range. In this work, we theoretically study excitation of SPPs in array of double-walled CNTs by electron beam. The most interesting specific features of the double-walled CNT modes are associated with the presence of interlayer modes enabling a strong confinement of the electromagnetic field between the nanowalls of CNT and thus providing a high deceleration coefficient at a relatively low absorption coefficient at the frequencies up to 40–50 THz. Due to the strong SPP confinement between nanowalls the neighboring CNTs have almost no effect on each other. Array of double-walled CNTs ensuring an effective conversion of the external pump energy into the SPP energy can be employed for design of slow-wave plasmonic nanostructures.
The possibility of surface plasmon polaritons (SPPs) amplification and generation in a waveguiding system containing single-walled carbon nanotube (CNT) and dielectric substrate is investigated. The SPP amplification is created by applying direct current in the CNT. Using numerical simulation, the effect of the substrate on the SPP characteristics in CNT was studied and it was shown that for a substrate with a high refractive index, the SPP amplification is realized at a lower drift velocity of free carriers of the pump current. For realization of the feedback in the CNT it is proposed to use the substrate with a periodic modulation of the dielectric function.
The generation of slow surface plasmon polaritons in a single-walled carbon nanotube is investigated theoretically. A mechanism of amplification of surface plasmon polaritons is based on the direct transfer of electromagnetic energy from a drift current in the nanotube into a surface wave.
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