The growing interest in the low-dimensional structures research has necessitated the development of non-contact optical methods for their thermal properties measurement. Thermoreflectance method allows thermal conductivity evaluation based on the analysis of material reflection coefficient change due to the laser radiation absorption and subsequent heating of the sample. Transient thermoreflectance in the frequency-domain (FDTR) and in the time-domain (TDTR) are already widely used for such measurements. More recent steady-state thermoreflectance method (SSTR) has the advantage above TDTR and FDTR which lies in the possibility to perform direct measurements resulting in higher accuracy and ease of measurement procedure. The current work is dedicated to the development of the approach for SSTR technique simulation. It includes the description of experimental procedure and the data collection, analytical and numerical data processing, finite elements simulation and the verification of the results. The proposed methodology has been performed on the example of 3 samples: Ge, Si, GaAs. The experiment included the measurement of the radiation power absorbed and reflected by the samples. Then, analytical and numerical models have been derived and used to calculate absorption and reflection coefficients taking in account Fabry-Pérot effect. The finite elements model has been carried out to simulate electromagnetic heating of the studied samples and to evaluate their temperature. The model took into the consideration a normal distribution of a laser beam its diameter. For the model validation the temperature maps captured by a thermal imager have been compared with the numerically simulated ones. The discrepancy did not exceed 9%. The performed approach can be used for SSTR setup calibration and analysis of thermal processes in the samples under study.
The terahertz (THz) frequency range is electromagnetic radiation in the range from 0.1 to 10 THz, which has high potential for use in non-destructive testing and control of the moisture content of objects. For a long time there was no elemental base of elements (receivers, transmitters, modulators, etc.) to work in this range. At the moment, existing detectors are made according to difficult and inaccessible technologies (like as molecular-beam epitaxy). In this paper, terahertz detector based on a thin-film structured thermoelectric material (solid solution of bismuth-antimony with a concentration of antimony of 12%) and copper contacts on a mica substrate was numerically demonstrated.
Magneto-optic Faraday effect in unaligned single-wall carbon nanotube thin films with different geometric parameters on transparent float glass substrates was experimental studied in a frequency range 0:2–0:8 THz (corresponding to a range from ~1:50mm to ~0:37mm) at a controlled room temperature of 291–293K, and a relative humidity of 40–45%. A change of 15° in an azimuth angle, and of 10° in an ellipticity angle was achieved. The results show that by using carbon nanomaterials-based structures it is possible to devise efficient tunable polarizers that can be used in the advanced areas of terahertz nanophotonics.
Now, terahertz (THz) technologies have been actively studied and applied in various biomedical applications including cancer diagnosis. It is related with unique features of THz spectroscopy, such as high sensitivity to water and other polar molecules, the presence of resonant peaks of various biomolecules in the THz frequency range, harmless of THz radiation to biological tissues. In this work, we have investigated different types of gastric tissues using THz spectroscopy and obtain refractive indices in the frequency range from 0.2 to 1 THz. Fourier transform infrared spectroscopy (FT-IR) was also applied in order to see what’s components of tissues make the most significant contribution in optical response and, therefore, allow to discriminate cancer.
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.
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.
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 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.
Magneto-optic Faraday effect in unaligned single-wall carbon nanotube thin films with different geometric parameters on transparent float glass substrates was experimental studied in a frequency range 0:2–0:8 THz (corresponding to a range from ~1:50mm to ~0:37mm) at a controlled room temperature of 291–293K, and a relative humidity of 40–45%. A change of 15° in an azimuth angle, and of 10° in an ellipticity angle was achieved. The results show that by using carbon nanomaterials-based structures it is possible to devise efficient tunable polarizers that can be used in the advanced areas of terahertz nanophotonics.
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.
Terahertz time-domain spectroscopic polarimetry (THz-TDSP) method was used to experimental study polarization properties of unaligned single-wall carbon nanotube thin films with different geometric parameters on transparent float glass substrates in a frequency range 0.2-0.8 THz at a controlled room temperature of 291–293K, and a relative humidity of 40–45%. Frequency dependences of azimuth and ellipticity angles of a polarization ellipse of electromagnetic waves transmitted through the samples were obtained for values of 0.2–1:.0Wcm-2 of an external 980nm near infrared optical pumping, with an external static magnetic field of ~0:3T. A change of 15° in the azimuth angle, and of 10° in the ellipticity angle was achieved. The results show that by using carbon nanomaterials-based structures it is possible to devise efficient and affordable magneto-optically tunable polarization modulators that can be used in the advanced areas of terahertz nanoscience and nanotechnologies.
To evaluate, calibrate equipment, and check the safety of THz devices etc, biotissue phantom is needed for these purposes. Although various researches about biotissue phantom using water have been done, such phantoms are not ideal. Because of the evaporation of water, the optical properties of a phantom change as the time goes by, since THz radiation is very sensitive to the water concentration of the sample. We chose graphite as the substitute of water, and therefore the water-free biotissue phantom was developed to mimic the similar optical properties as human tissues. In order to determine the concentration of each component precisely, quantitative analysis is needed. In this work, we used several mathematical models of the effective medium theory, including the Polder and van Santen model, the Landau, Lifshitz, Looyenga model, the model of complex refractive index, and the Bruggeman model, to study the influence of different graphite concentrations on the refractive index of the water-free biotissue phantom. Phantoms with different graphite concentrations were simulated and 3 phantoms with different graphite concentrations were produced to evaluate the reliability of each model. The fabricated phantoms were then compared with stomach tissues. The result also shows the promise that by using the proper mathematical model, correct concentration can be calculated for other tissue phantom.
Non-invasive diagnostics methods are very helpful for cancer diagnosis and they are a research hotspot in the field of biomedicine. Terahertz (THz) photonics is an emerging technology that can be applied in the field of medical diagnostics. This is due to unique features of THz radiation such as harmlessness to biological tissues, strong absorption by water, ability to identify various biomolecules, etc. In this work we have investigated different types of normal and cancer fresh tissues of the stomach using terahertz time domain spectroscopy in reflection mode. Refractive indices of mucous, serous and tumor stomach tissues were obtained in the frequency range of 0,2 - 1 THz. These optical properties are higher for cancer tissue than for mucosa and lower than for serosa. Thus possibility of discrimination of tumor from normal stomach tissue was demonstrated. This study has practical significance for the field of clinical cancer diagnosis and will help to better understand the specifics of the method of pulsed THz spectroscopy applicable to this field.
This paper presents qualitative analysis of terahertz time-domain spectroscopy application for cancer diagnosis by measurement of the optical properties and spectral characteristics of cancer cells. For this purpose, the cultivation of two cancer cells, U-251 (glioblastoma brain) and A549 (lung adenocarcinoma), were carried out, then their refractive index, absorption coefficient and dielectric constant were measured, and the optical properties of tumor cells were compared with the optical properties of healthy cells (fibroblasts). Tumor cells contain more OH-components in comparison with healthy cells. Since terahertz radiation is heavily absorbed by water, there are differences in the spectra of healthy and oncological cells. To obtain the optical properties and spectral characteristics of the researched objects, a terahertz time-domain spectroscopy method in the transmission mode was used. The researched cell lines were cultured in vitro. Optical properties and spectral characteristics of the samples were calculated by the thin film method and Fourier transform. The results show the differences of refractive index, absorption coefficient and dielectric permittivity between the oncological cell lines U- 251, A549 and the healthy cells in the frequency range 0.2-1 THz. It was found that cancer cells have higher values of refractive indices and absorption coefficients than those of healthy cells. Brain glioblastoma (U-251) has a transmission peak at the frequency of 0.24 THz. The results obtained in this work can form the basis for the diagnosis of brain and lung cancer with the use of terahertz time-domain spectroscopy.
The paper presents the results of the studies of influence of optical radiation with wavelengths of 520 and 780 nm on human glial cells (U251) at the range of exposure times ~ 1-15 min. It was found that after the first minute of irradiation at the wavelength of 780 nm, the relative number of apoptotic cells significantly increased. The result corroborates the concept of biological hazard of optical radiation for tumor cells, and suggests that the approach has a great potential in clinical application for the treatment of human glioma.
The glucose level of blood can be obtained by terahertz time-domain spectroscopy using refractive index measurement method. The detected refractive indices vary from person to person since the impact of bilirubin and creatinine wasn’t considered. 14 human blood samples were tested using terahertz time-domain spectroscopy. The experiment results show that under the certain concentration of glucose, the refractive index of blood decreases with the increase of bilirubin and creatinine concentration, and thus the concentration of other blood components may also influence on the refractive index of blood. The feasibility of using terahertz time-domain spectroscopy to determine the level of glucose, bilirubin and creatinine qualitatively and quantitatively is provided.
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.
In this work, we study infrared optical pump-induced changes in terahertz conductivity of multi-layer graphene on a silicon substrate using terahertz time-domain spectroscopy. Results indicate that the conductivity and optical parameters of investigated material strongly depend on a pumping intensity and the presence of FeCl3 molecules intercalation. The findings are helpful for determining the most optically tunable material towards designing of optically controllable terahertz devices based on new two-dimensional material beyond graphene monolayer.
This work is devoted to investigation of optical properties (dispersion of refractive index, permittivity and absorption coefficient) of human nails in THz frequency range. These data were obtained by THz time-domain spectroscopy (TDS) technique in transmission mode. These results may be used to develop non-invasive technique of human pathologies control using nail as reference sample in reflection mode of THz TDS.
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