Efficient devices for control properties of electromagnetic waves are essential for the development of terahertz (THz) technologies. But despite the great progress achieved in a study of graphene, the influence of the number of graphene layers on its properties in the THz frequency range has not yet been sufficiently studied. In this work, we experimentally studied properties of multilayer graphene (MLG) films in the frequency range 0.2–0.8 THz, at a room temperature, and a relative humidity of 40%. Using our custom-made THz time-domain spectroscopic polarimetry system, we obtained spectra of the complex relative permittivity and the electrical conductance of the chemical vapor deposition graphene with ∼14, ∼40, and ∼76 layers of graphene on glass substrates. It is shown that the conductance increases nonlinearly with an increase in the graphene layer number and reaches, for ∼76 layers, 0.06 S for the real, and 0.03 S for the imaginary part, respectively.
Petroleum products are the largest source of energy in the world, accounting for over 30% [1]. The amount of oil production increases annually, as does the production of petroleum products. In 2015, 4181 million tons of petroleum products were manufactured, and in 2018, 4350 million tons were produced [2]. It becomes necessary to analyze oil and oil products to determine their quality. The traditional chemical method for analyzing crude oil and petroleum products requires a large number of instruments, as well as a lot of time and consumables [3-5]. To speed up the process of determining the quality of oil products, it is possible to perform spectral analysis using terahertz time-domain spectroscopy. The optical properties obtained using terahertz spectroscopy in the time domain of a petroleum product can be used to analyze its quality. At the moment, there are studies of crude oil for the presence of asphaltenes and their effect on the optical properties of crude oil [6]. The absorption coefficient spectrum of crude oil shows moderate absorption due to asphaltene with no clear indications, except for some narrow absorption lines, which are caused by water molecules adsorbed on the asphaltene. Other research focuses on petroleum products, namely oils, gasoline and diesel [7]. As a result, oils have a high absorption coefficient at high frequencies, the same results were observed for gasoline and diesel fuel. This work is devoted to the spectral analysis of a mixture of gasoline with an octane rating of 98 and diesel fuel, depending on the concentration of gasoline, using terahertz time-domain spectroscopy.
The influence of antimony content x and a film thickness on dynamical terahertz conductivity and galvanomagnetic properties of thin-film bismuth antimonides Bi1-xSbx at room temperature is studied in this work by means of terahertz time-domain spectroscopy and galvanomagnetic measurements. It is shown that thin bismuth-antimony films have tunable optical response in the THz frequency range. The hyperbolic permittivity dispersion of an effective film-on-substrate structure is also reported. The studied thin-film materials can be applied in detection of terahertz radiation and in terahertz filtering, modulation, phase and polarization shifting, in sensing, imaging and communication systems which work at normal conditions.
Significance: A new concept of a biotissue phantom for terahertz (THz) biomedical applications is needed for reliable and long-term usage.
Aim: We aimed to develop a new type of biotissue phantom without water content and with controllable THz optical properties by applying graphite powders into a polyvinyl chloride plastisol (PVCP) matrix and to give a numerical description to the THz optical properties of the phantoms using the Bruggeman model (BM) of the effective medium theory (EMT).
Approach: The THz optical properties of graphite and the PVCP matrix were measured using THz time-domain spectroscopy, which works in the frequency range from 0.1 to 1 THz. Two phantoms with 10% and 12.5% graphite were fabricated to evaluate the feasibility of describing phantoms using the EMT. The EMT then was used to determine the concentration of graphite required to mimic the THz optical properties of human cancerous and healthy oral tissue.
Results: The phantom with 16.7% of graphite has the similar THz optical properties as human cancerous oral tissue in the frequency range of 0.2 to 0.7 THz. The THz optical properties of the phantom with 21.9% of graphite are close to those of human healthy oral tissue in the bandwidth from 0.6 to 0.8 THz. Both the refractive index and absorption coefficient of the samples increase with an increase of graphite concentration. The BM of the EMT was used as the numerical model to describe the THz optical properties of the phantoms. The relative error of the BM for the refractive index estimation and the absorption coefficient is up to 4% and 8%, respectively.
Conclusions: A water-free biotissue phantom that mimics the THz optical properties of human cancerous oral tissue was developed. With 21.9% of graphite, the phantom also mimics human healthy oral tissue in a narrow frequency range. The BM proved to be a suitable numerical model of the phantom.
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
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