Dynamical manipulation of electromagnetic radiation in arbitrary manner is achievable through metasurface utilization. Significant issue for practical applications of metasurfaces is in solving inverse problem, i.e. prediction of metasurface pattern dimensions in accordance to the desired electromagnetic response. In this work, we propose the approach based on equivalent circuit model enabling to connect resonant features of metasurface with its geometry dimensional parameters.
Metasurface with periodic subwavelength resonators, placed on dielectric substrate is one of the main research interests in the terahertz (THz) photonics. Based on metal/graphene hybrid materials such structures can achieve giant tunable asymmetric transmission and circular dichroism (CD). In this paper we discuss a circular dichroism of metasurfaces consisted of resonators with n-fold rotational symmetry Cn, i.e. C2, C3, C4. The numerical simulation was performed using CST Microwave Studio. Theoretical analysis combines symmetry restrictions in effective polarizability approximation for calculation of transmission and reflection coefficients. The numerical simulation was done in the millimeter wave range. This research has both fundamental and applied relevance, and may be used in development of terahertz and microwave devices, such as waveplates, polarization sensitive absorbers, etc.
Terahertz time-domain spectroscopy is a unique spectroscopic technique that determines amplitude and phase change resulting from terahertz wave interaction with material. The method terahertz time-domain polarimetry may be an alternative method. It is a characterization technique in which the change of polarization state of the wave transmission through the sample is measured. We propose analytical description of extraction the diagonal and off-diagonal components of permittivity tensor of materials in the terahertz frequency range using terahertz time-domain polarimetry. Using the diagonal and off-diagonal components of the permittivity tensor of materials, the effective mass, Hall mobility, and scattering time can be calculated.
In this work, amplitude modulator of terahertz radiation was fabricated and experimentally studied. The sample consists of two plastic substrates, internally coated with multilayer graphene, the cavity between the plates was filled with ion gel. The fabricated sample was studied by terahertz time-domain spectroscopy method. In the experiment, waveforms of terahertz pulse transmitted through the sample at different applied DC voltage were obtained. It was shown that with increasing DC voltage, the amplitude of the transmitted terahertz radiation decreases. The results may be used to design attenuators and modulators for terahertz communication.
At present, due to the rapid development of THz technology in medical applications, it becomes urgent to develop stable test objects (phantoms) for calibration, optimization of the operation of devices, and verification of the research methods used. In this work, a five-component phantom has been developed based on water, glycerin, starch, bentonite, and gelatin, and it was shown that these phantoms can be used as indicators of the level of dehydration of the renal tumor tissue. The mechanical properties of the phantom were investigated, the dispersions of the refractive index and absorption coefficient of the biocomposite were determined in the range from 0.2 to 1 THz. To simulate the optical parameters of a phantom depending on the concentration of inclusions, an iterative method was developed and it was found that this method makes it possible to simulate the optical parameters of a phantom at low concentrations of bentonite. It is shown that in the structure of a five-component phantom, during fabrication, clusters of starch particles are formed, and the resonant interaction of the incident THz radiation with cluster particles leads to the excitation of whispering gallery modes.
The terahertz optical properties of composites with poly vinyl chloride (PVC) nanofibers and polypropylene (PP) were investigated. To evaluate the influence of PVC content, we measured the composites under conditions where the content of PVC nanofibers was controlled. We found that the refractive indices increase with the decrease of PVC nanofiber content. We also found that highly aligned PVC nanofibers bring birefringence to the composites. The proposed PVC-PP composites are promising materials for terahertz optics.
Recent years, polarimetry in the terahertz frequency range has gained popularity. Polarimetry is a technique used to measure the polarization state of electromagnetic waves transmitted through samples. The ellipticity angle, the azimuth rotation angle, complex optical properties of materials can be obtained by terahertz timedomain polarimetry. This allows for obtaining more comprehensive information about the object. In this paper, we study diagonal and off-diagonal components of the permittivity tensor of thin bismuth-based films using terahertz time-domain polarimetry
We propose a modified approach to more detailed study of gyrotropic materials using terahertz (THz) ellipsometry method based on the magneto-optical Kerr effect (MOKE). This approach allows to obtain polarization properties and to calculate the permittivity tensor of materials which are reflective or opaque in THz frequency range. The method allows to measure any values of the diagonal and off-diagonal components of the permittivity tensor and can be used for materials with a strong magneto-optical response.
An emission illusion device based on metamaterials with the cylindrical polar angle-dependent tensors of permittivity and permeability was proposed and analyzed. The illusion effect was numerically simulated using the finite-element method for a point source. The influence of metamaterial anisotropy and radiation source position on the illusion effect was studied.
The work is dedicated to design of epsilon-near-zero metamaterials (ENZ) in terahertz frequency range. Two materials were investigated: the first material is the one-layered single-wire medium (SWM) and the second material consists of the planar parallel metal stripes on the layer of polyethylene terephthalate (PET). The wired medium was designed using analytical approximation of thin wire structures and verified by numerical simulations. The striped metamaterial was designed using numerical simulations software and its performance was experimentally verified by terahertz timedomain spectroscopy.
Recent decades metamaterials in terahertz frequencies become very popular in the scientific society. Metamaterials is an arrangement of artificial structural elements (unit cell) that gives properties which cannot be found in nature. The effective properties of metamaterials depend on their design. This fact provides a big variety in applications of metamaterials as filters, absorbers, polarizers, etc.
In this work we have studied the influence of the chiral metasurface resonator conductivity on polarizing properties of the metasurface. The unit cell of the metasurface consists of metallic gammadion crosses on both sides of the dielectric substrate. The petals of the upper resonators were partly made of different metals. Each combination of metals in design of the resonator leads to a difference in transmission of the metasurface. Due to chirality, transmission coefficients for left- and right-handed polarized waves are different. This phenomenon causes changes in the polarization ellipse of transmitted wave. The metasurface was numerically simulated using CST Microwave Studio by finite-elements method in frequency domain. The virtual experiment shows a difference in ellipticity and azimuth polarization rotation angle spectra of resonators with different conductivity. These results provide usage of materials with changeable conductivity, for example, graphene, in development of tunable polarization converter.
The investigated metasurface might be used in terahertz polarimetry of cancer, teeth and skin deceases. These measurements can be performed by terahertz time-domain spectroscopy.
The polarizing properties of chiral metasurface made of planar array of gammadion crosses placed on silicone
substrate were investigated in the frequency range of 0.1-0.3 THz. The ability of polatization properties control
of metasurface working as elliptic polarizer by gammadion petal width changing was shown.
This paper presents an investigation of terajets formation by dielectric periodic structure at terahertz frequencies in effective medium regime (photonic metamaterial). The dispersions of effective permittivity for three periodic structures formed by different types of plastics (ABS, PLA, Crystal) were analytically obtained for both regimes. Numerical simulation of this structure was performed by using COMSOL Multiphysics. The terajet formation was numerically shown.
The excitation of surface plasmon polariton at the interface of left-handed metamaterial with cylindrical anisotropy and
dielectric medium in THz frequency range was considered. The impact of wave polarization and incidence angle was
considered.
The analytically realization of electromagnetic wave frequency conversion in a time-varying medium was shown by the two methods. The first method considers the optical analog of the electromagnetic wave redshift in the expanding universe using the transformation optics mathematical approach. The second one describes the transient process of pulse electromagnetic wave interaction with the time-varying medium using method of the second order Volterra integral equation. The frequency conversion was shown for several types of commercial laser wavelengths.
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