Properties Of Terahertz Waves Research Articles

Design of THz Refractive Index-Based Diamond Shaped Biosensor Using Gated Axial Attention Network for MTB Detection

MTB is usually diagnosed using sophisticated and expensive methods that include molecular and microscopic examination, making the process tedious and lengthy. This research proposes an innovative approach to enhance MTB detection through a novel biosensor design that integrates Terahertz refractive index measurements with a Gated NasNet Running City Game Axial Attention Network. The proposed diamond-shaped biosensor harnesses the unique properties of Terahertz waves to measure refractive index variations in biological tissues, specifically targeting MTB infections. A thorough optimization process was carried out to obtain an optimal sensor design, which included optimizing several design aspects such as size and materials. The sensor exhibits exceptional characteristics, including processing time of 0.1 s for 40000 iterations and 0.04 Confinement loss among other models. To optimize the weight parameters and reduce computational complexity, the Gated NasNet Running City Game Axial Attention Network is integrated into this research. The model demonstrates impressive performance of nearly 99.1% sensitivity in detecting MTB. The exceptional results indicate the substantial capability of the proposed biosensor for quick and accurate detection of MTB. The sensor’s exceptional performance metrics, along with its simple design, signify a significant breakthrough in the realm of biosensing technology.

Development and Prospects of Terahertz Photodetector

Terahertz photodetectors show great potential in the fields of optical communication, security inspection, and nondestructive testing. This paper firstly outlines the properties of terahertz waves; further describes the detection mechanism and preparation materials; further discusses its applications in security inspection imaging through packaging materials, indoor local area wireless communication, high speed local area communication, space communication and confidential communication; finally summarizes and outlooks, the possible development directions of terahertz photodetectors are to study new materials with excellent optoelectronic properties at room temperature, to combine different sizes or different kinds of materials combined, the use of antennas to improve the coupling efficiency of terahertz radiation, and the design of new device structures. It can be foreseen that terahertz technology will have a profound impact on science and technology, economy and national security.

Study on the propagation properties of terahertz waves in spacecraft dusty plasma sheath

Terahertz (THz) wave transmission in non-uniform dielectric layer containing dusty plasmas and aluminum (Al) is investigated by using the Wentzel–Kramer–Brillouin method. The application of magnetic field and increase in electromagnetic waves frequency are up-and-coming solutions for the “blackout” issue. Therefore, this work considers the effect of external magnetic field and electron density distribution. The electron density distributions are assumed to be double Gaussian profile, uniform distribution, Epstein distribution, and both right- and left-hand circularly polarized waves are analyzed. Then the effects of physical parameters and THz frequency on the transmission properties are analyzed. Results show that the presence of Al can shield electromagnetic waves, but we can still control THz waves in lower frequency band to achieve communication. By adjusting THz waves frequency and plasma parameters, waves can pass through the Al plasma sheath effectively under certain circumstances. It is expected to mitigate the blackout issue of hypersonic spacecraft.

Plasmonic vortex beam emitter

Terahertz vortices prompt numerous advanced applications spanning classical and quantum communications, sensing, and chirality-based detection, owing to the inherent physical properties of terahertz waves and orbital angular momentum (OAM). Nonetheless, existing methodologies for generating terahertz vortices face challenges such as unalterable topological charges and intricate feed networks. To address these limitations, we propose a novel approach to generate multi-mode and tunable vortex beams based on chiral plasmons. Through eigenmode analysis, the uniform helical gratings are demonstrated to support chiral plasmons carrying OAM. By leveraging their vortex characteristics and introducing modulation into the periodic system, these chiral plasmons are alternatively diffracted into high-purity vortex radiations according to the Bragg law. To validate the theory, the vortex beam emitter is fabricated and measured in the microwave regime based on the modulated scheme. Experimental results confirm the emission of vortex beams with desirable phase distributions and radiation patterns. Our findings highlight the potential of chiral plasmons as seeds for tunable and compact vortex radiation, offering promising applications in tunable vortex sources.

FDTD Simulation on Terahertz Waves Propagation Through a Dusty Plasma**supported by National Natural Science Foundation of China (Nos. 41104097, 11504252, 61201007, 41304119), the Fundamental Research Funds for the Central Universities (Nos. ZYGX2015J039, ZYGX2015J041), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20120185120012)

The frequency dependent permittivity for dusty plasmas is provided by introducing the charging response factor and charge relaxation rate of airborne particles. The field equations that describe the characteristics of Terahertz (THz) waves propagation in a dusty plasma sheath are derived and discretized on the basis of the auxiliary differential equation (ADE) in the finite difference time domain (FDTD) method. Compared with numerical solutions in reference, the accuracy for the ADE FDTD method is validated. The reflection property of the metal Aluminum interlayer of the sheath at THz frequencies is discussed. The effects of the thickness, effective collision frequency, airborne particle density, and charge relaxation rate of airborne particles on the electromagnetic properties of Terahertz waves through a dusty plasma slab are investigated. Finally, some potential applications for Terahertz waves in information and communication are analyzed.

Transmission properties of terahertz waves through asymmetric rectangular aperture arrays on carbon nanotube films

Transmission spectra of terahertz waves through a two-dimensional array of asymmetric rectangular apertures on super-aligned multi-walled carbon nanotube films were obtained experimentally. In this way, the anisotropic transmission phenomena of carbon nanotube films were observed. For a terahertz wave polarization parallel to the orientation of the carbon nanotubes and along the aperture short axis, sharp resonances were observed and the resonance frequencies coincided well with the surface plasmon polariton theory. In addition, the minima of the transmission spectra were in agreement with the location predicted by the theory of Wood’s anomalies. Furthermore, it was found that the resonance profiles through the carbon nanotube films could be well described by the Fano model.

Optically tuned terahertz modulator based on annealed multilayer MoS2.

Controlling the propagation properties of terahertz waves is very important in terahertz technologies applied in high-speed communication. Therefore a new-type optically tuned terahertz modulator based on multilayer-MoS2 and silicon is experimentally demonstrated. The terahertz transmission could be significantly modulated by changing the power of the pumping laser. With an annealing treatment as a p-doping method, MoS2 on silicon demonstrates a triple enhancement of terahertz modulation depth compared with the bare silicon. This MoS2-based device even exhibited much higher modulation efficiency than the graphene-based device. We also analyzed the mechanism of the modulation enhancement originated from annealed MoS2, and found that it is different from that of graphene-based device. The unique optical modulating properties of the device exhibit tremendous promise for applications in terahertz switch.

Propagation Properties of Terahertz Waves in a Time-Varying Dusty Plasma Slab Using FDTD

The complex dielectric permittivity of a dusty plasma, which contains an inhomogeneous electron density, charging response factor, and dust charging frequency caused by dust particles, is given to simulate the time-varying dusty plasma sheath. The recurrence field and current equations for terahertz (THz) wave propagation in the plasma are deduced and discretized using the auxiliary differential equation finite-difference time-domain (ADE-FDTD) method. The reflection, transmission, and absorption coefficients of a time-varying dusty plasma slab are calculated by using the ADE-FDTD method. The numerical results indicate that the reflection coefficients of the slab are easily affected by the rise time of the electron density. Besides, the absorption coefficients increase with the decrease in the rise time and working frequency as well as with the increase in the densities of electrons and dust particles. It is shown that THz waves may have potential applications in radio communications with a spacecraft at its re-entry into the atmosphere.

High speed optical modulation of terahertz waves using annealed silicon wafer

Modulation properties of terahertz waves going through a light excited high resistivity silicon wafer are analyzed and measured. Free carrier lifetime of the silicon wafer affects the modulation depth and speed of the terahertz wave. The lifetime is reduced to less than 1 μs by thermal processing for high speed modulation. Experimental results show that the response time and modulation depth of the proposed modulating structure are close to 1 μs and 51%, respectively.

Effect of additives on the large-size growth of 4-N,N-dimethylamino-4-N-methyl stilbazolium naphthalene-2-sulfonate (DSNS) single crystal: an efficient stilbazolium derivative NLO crystal with potential terahertz wave properties.

We explored the growth of the highly nonlinear optical stilbazolium salt 4-N,N-dimethylamino-4-N-methyl stilbazolium naphthalene-2-sulfonate (DSNS) by a slow evaporation method.

Creation of Titania Artificial Interfaces with Geometric Patterns by Using Microstereolithography and Aqueous Solution Techniques

Titania micropatterns with periodic arrangements were successfully formed on glass substrates for use with electromagnetic wave energy resonance and localizations in terahertz frequency ranges. Geometric arrangements of acrylic polygonal tablets with titania particle dispersions were fabricated by using micropatterning stereolithography. Moreover, periodically arranged full anatase‐phase titania tablets were created homogeneously through liquid‐phase crystal depositions of water solvent processes, using microtemplates fabricated by using the stereolithography system. The terahertz wave properties were measured and calculated by using a time‐domain spectroscopic system and finite‐difference time‐domain method.

Creation of Titania Artificial Interfaces with Geometric Patterns by Using Micro Stereolithography and Aqueous Solution Techniques

Titania micro patterns with periodic arrangements were formed on glass substrates successfully for electromagnetic wave energy resonations and localizations in terahertz frequency ranges. Geometric arrangements of acryl polygon tablets with titania particles dispersions by using micro patterning stereolithography. Moreover, periodically arranged full titania tablets with anatase phase were created homogeneously though liquid phase crystal depositions of water solvent processes under micro templates fabricated by using the stereolithography system. The terahertz wave properties were measured and simulated by a using time domain spectroscopic system and finite difference time domain method. The terahertz waves having micrometer order wavelengths and belonging in far-infrared frequency ranges are expected to apply for various types of novel sensors which can detect micro cracks on materials surfaces, micro defects in electric devices, bacteria in foods, and cancer cells in human skins.

Terahertz time domain spectroscopy of epoxy resin composite with various carbon inclusions

The propagation properties of terahertz waves through epoxy resin filled with small amounts (0.25–1.5wt.%) of commercially available carbon black (CB) and CVD made single-walled and multi-walled carbon nanotubes (CNT) have been investigated by terahertz time domain spectroscopy. High electromagnetic attenuation specified substantially with absorption of THz radiation and strongly decreasing with the decrease of frequency from 0.2 to 1.5THz has been found for both types of CNT fillers starting from 1wt.% of nanocarbon concentration. At the same time CB in the same concentration does not make any impact to THz transmission spectrum. The resonance dielectric dispersion has been observed for all investigated samples, which can be attributed to phonon resonance in epoxy resin matrix. The availability of Maxwell–Garnett model for epoxy resin filled with 0.25–1.5wt.% of CNT was also addressed in the paper.

Investigation of the propagation properties of terahertz waves through a semiconductor subwavelength slit

The propagation properties of terahertz (THz) waves through semiconductor conductor–dielectric–conductor (CDC) structure have been investigated. The influence of geometrical parameters, radiation frequencies and temperatures on the propagation properties have been shown and discussed. The contour results demonstrate that as the length of the dielectric filling materials increase, the effective indices of the propagation modes increase. Compared with the results of the metal structure, the effective indices of surface modes through semiconductor InSb slits increase, the propagation length decrease. The effective indices of the surface modes decrease, the propagation lengths increase with the increasing of the carrier concentration. It is expected that the numerical results may be very helpful to have better understand the propagation mechanism of THz waves through semiconductor subwavelength slit.

Comparison of the reflection properties of a metal wire in the visible spectral and terahertz regime

The reflection properties of terahertz waves propagating along a metal wire are investigated and compared with the results in the visible spectral regime. The effects of metal wire radii, radiation frequencies and dielectric surrounding materials on the reflection characteristics are given and discussed. The contour plots show that as radiation frequency increases, the reflection amplitude decreases, and the reflection phase increases. With an increase in metal wire radius, the reflection amplitude decreases, and the reflection phase increases. The results are very useful for the application of metal wire antennas and plasmonic resonators.

Investigation of terahertz surface waves of a metallic nanowire

The influence of the nonlocal effect on the optical properties of terahertz waves propagating along a metallic nanowire has been investigated, taking into account the effects of the composed materials, metal wire radii, and radiation frequencies. The results manifest that the nonlocal effect has significant influence on the propagation properties of terahertz nanowire surface waves. The contour results show that as metal wire radii increase, the phase velocity increases, and the attenuation losses decrease. On condition that the metallic nanowire radius is small (tens of nanometers), the attenuation losses of the surface waves decrease with the increasing of frequency. The numerical results are very useful for the development of nanoplasmonic devices in the fields of terahertz spectroscopy, biological sensors, and detectors.

Terahertz Wave Properties of Ceramic Photonic Crystals with Graded Structure Fabricated by Using Micro-Stereolithography

Fabrication and terahertz wave properties of alumina micro photonic crystals with a diamond structure were investigated. The three-dimensional diamond structure was designed on a computer using 3D-CAD software. Acrylic diamond structures with alumina particles dispersion were formed by using micro-stereolithography. Fabricated precursors were dewaxed and sintered in the air. The electromagnetic wave properties were measured by terahertz time-domain spectroscopy. A complete photonic band gap was observed at the frequency range from 0.40 to 0.47 THz, and showed good agreement with the simulation results calculated by the plane wave expansion method. Moreover, a localized mode was obtained by introducing a plane defect between twinned diamond structures. The one-way transmission of the electromagnetic wave was realized by using this twinned photonic crystal with the graded diamond structure. They corresponded to the simulation by the transmission line modeling (TLM) method.

Analysis of the extraordinary transmission properties of arrays of subwavelength holes on a metal film in the terahertz region

The extraordinary transmission properties of terahertz waves through arrays of subwavelength holes on a metal film have been investigated. The effects of the geometrical parameters and dielectrics filling the hole on transmission properties have been explored. The results show that the resonance peak shifts to long wavelength as the hole width and lattice period constant increase. As the refractive index of the dielectric materials filling the hole increases, the transmittance increases and the resonance peak wavelength changes to low frequency. The phase retardation can be flexibly changed by varying the geometrical parameters and dielectric materials filling in the hole.

Terahertz Wave Control Using Ceramic Photonic Crystals with a Diamond Structure Including Plane Defects Fabricated by Microstereolithography

The fabrication and terahertz wave properties of alumina microphotonic crystals with a diamond structure were investigated. Acrylic diamond structures with alumina particles' dispersion were formed using microstereolithography. Fabricated precursors were dewaxed and sintered in air. The electromagnetic wave properties were measured by terahertz time‐domain spectroscopy. A complete photonic band gap was observed from 0.40 to 0.47 THz, and showed good agreement with the simulation of a plane wave expansion method. Moreover, a localized mode was observed by introducing a plane defect between twinned diamond structures. The localized mode was analyzed using transmission line modeling simulation.

Terahertz wave properties of alumina microphotonic crystals with a diamond structure

Fabrication and terahertz wave properties of alumina microphotonic crystals with a diamond structure were investigated. The three-dimensional diamond structure was designed on a computer using 3D-CAD software. The designed lattice constant was 500 μm. The structure consisted of 8 × 8 × 4 unit cells. Acrylic diamond structures with an alumina dispersion of 40 vol% were formed by using microstereolithography. Fabricated precursors were dewaxed at 600 °C and sintered at 1500 °C. The linear shrinkage ratio was about 25%. The relative density reached 97.5%. The electromagnetic wave properties were measured by terahertz time-domain spectroscopy. A complete photonic band gap was observed at the frequency range from 0.40 THz to 0.47 THz, and showed good agreement with the simulation results calculated by the plane wave expansion method. Moreover, localized modes were obtained at the frequencies 0.42 THz and 0.46 THz by introducing an air defect in the diamond structure. They corresponded to the simulation by the transmission line modeling method.