Frequency-tunable Terahertz Wave Research Articles

An ion-charged carbon nanotube oscillator beyond the terahertz regime

A frequency-tunable nano-oscillator consisting of a K+ ion and a negatively-charged carbon nanotube (CNT) was proposed. The ion induces a strong dielectric response on the wall of the CNT, which can be described through a self-consistent classical molecular dynamics based on the atomistic moment method. The calculation results indicate that the stability and the oscillating frequency of the oscillator strongly depend on the quantity of charge on the CNT. As the extra charge on the CNT increases, the oscillator becomes more stable, and the oscillating frequency increases successively, from 0.23 to 1.31 THz. The high frequency and stability of the system are due to the strong axial Coulomb restoring force and its small fluctuations in the cross section of the CNT. This kind of nano-oscillator can be used as a frequency-tunable terahertz wave detector.

Emission of continuous terahertz waves by high Tc superconductors

Continuous coherent terahertz waves have various kinds of application such as biology and information science. One of the hurdles for technical advancements in the terahertz region of electromagnetic wave is development of sources for intense and continuous coherent and frequency tunable terahertz waves. Therefore, we investigate a mechanism for emitting the terahertz waves by using high T c superconductors. High T c superconductors form naturally stacked Josephson junctions. In the junctions there appears an excitation called Josephson plasma, the frequency of which is in the range of terahertz. The frequency appears inside the superconducting main energy gap and the Landau damping is weak. Therefore, if the Josephson plasma is excited in someway, the excited plasma decays by emitting an electromagnetic wave. When an external current and a magnetic field are applied to the sample, fluxon flow induces a voltage. The voltage creates oscillation current through the Josephson effect, and the current excites the Josephson plasma waves with terahertz frequencies. In the present work we perform simulation of terahertz emission using Earth Simulator. We used the parameters corresponding to Bi 2Sr 2CaCu 2O 8+ δ and obtained the following results. The sample itself works as a cavity, and the input energy given by an external current is stored in a form of standing wave of the Josephson plasma. A part of the energy is emitted as terahertz waves. The emitting electromagnetic wave is continuous coherent terahertz waves with the power of an order of 1000 W/cm 2. The frequency is tunable by changing the applied current.

Widely Frequency-Tunable Terahertz Wave Generation and Spectroscopic Application

This paper discusses about the widely frequency-tunable THz-wave source is effective for spectroscopic analyses and THz imaging of various kinds of macromolecules like DNA-related molecules, cancers, viruses like SARS, bacteria as well as conformational changes of protein like BSE.

Frequency-tunable terahertz wave generation via excitation of phonon-polaritons in GaP

High-power, wide-frequency-tunable terahertz waves were generated based on difference-frequency generation in GaP crystals with small-angle noncollinear phase matching. The tunable frequency range was as wide as 0.5–7 THz, and the peak power remained high, near 100 mW, over most of the frequency region. The tuning properties were well described by the dispersion relationship for the phonon-polariton mode of GaP up to 6 THz. We measured the spectra of crystal polyethylene and crystal quartz with high resolution using this THz-wave source.

Frequency-tunable high-power terahertz wave generation from GaP

A frequency-tunable terahertz wave was generated from GaP crystals using an optical parametric oscillator as the pump source and a YAG laser (1.064 μm) as the signal source. By tuning the very small angle, θin, between the pump and signal light beam directions, tunable terahertz waves over the frequency range from 0.5 to 3 THz were obtained. The THz frequency changed almost linearly with the angle θin. The precise noncollinear phase matching condition is discussed. The pulsed peak power of the THz wave was as high as 480 mW at 1.3 THz.