Anton A. Yablokov

The use of measurements in several ranges leads to an increase in the reliability of the determination of substances in the compositions of multicomponent gas mixtures of various origins (detection of a substance in several ranges reliably confirms its presence in the studied mixture), which is relevant for various applications, including those actual for the medical diagnosis and control of the treatment of metabolites-markers of diseases and pathologies. In addition, it becomes possible to detect substances in a more convenient range for measurements. The aim of the work is to develop and implement a non-stationary gas spectrometer in the 75-110 GHz range with phase switching of radiation acting on the gas. The spectrometer concept is based on the use of commercially available devices and components. Test measurements were carried out using the example of acetonitrile, which has strong absorption lines in the operating range of the spectrometer. The developed and realized spectrometer complements the spectroscopic complex, which includes high-resolution gas spectrometers based on the effect of fast frequency swiping and phase manipulation of radiation acting on the gas in the frequency ranges 18-26 GHz, 118-175 GHz, as well as near 2 THz and 3.78 THz. In addition, besides developed software for measuring and processing the results obtained, a program has been written that allows the identification of experimentally measured absorption lines using freely available spectroscopic databases.

The work is devoted to studying the composition for grain (barley and wheat) by terahertz (THz) high-resolution gas spectroscopy. The comparison of the set of chemical compounds formed during thermal decomposition of grain and cereals produced from grain was carried out with using a high-resolution spectrometer with phase-switching of radiation in the range of 115-175 GHz acting on studied gas developed by the authors. Free online spectroscopy databases were used for identification of substances. The results of comparison of molecular profiles of gas mixtures of thermal decomposition products of two varieties of barley, pearl barley and one variety of wheat are presented. Good agreement of the molecular composition for barley and pearl barley and some difference from the composition of the mixture obtained by heating wheat are shown.

Subject of study. The subject of this study was the chemical composition of multicomponent gas mixtures of biological origin. Aim of study. This study aimed to construct the metabolic profiles of diseases by studying biological samples (tissues of ear-nose-throat organs, urine) with high-resolution terahertz (THz) spectroscopy. Method. Spectroscopy based on nonstationary effects, such as inducing and decaying the free dumping polarization in a gas sample during the interaction of radiation and gas molecules, is a highly sensitive method for investigating multicomponent gas mixtures. A spectrometer based on these principles operates in the modes with the phase switching or fast sweeping of the probing radiation. Main results. Some experimental results of using high-resolution THz spectroscopy for medical diagnostics and treatment control are presented in this paper. The multicomponent gas mixtures, such as vapors or thermal decomposition products of various samples [biological liquids (urine) and pathological tissues of living organisms], were studied using THz nonstationary spectrometers for developing diagnostic methods. The results of experimental data analysis reveal the markers for specified diseases of living organisms (diabetes, pathology tissues of ear-nose-throat organs) or substances appearing during therapeutic treatment (nephrotoxical influence of chemotherapy). Practical significance. THz nonstationary high-resolution spectroscopy can be considered a prospective analytical method of spectral analysis for fundamental and applied research.

Hafnium is a superconductor with a transition temperature slightly above 100 mK. This makes it attractive for such applications as microcalorimeters with high energy resolution. We report the superconducting properties of Hf films of thicknesses ranging from 60 to 115 nm, deposited on Si and Al₂O₃ substrates by electron beam evaporation. Besides that, we fabricated and measured combinations of hafnium with thin layers of normal metals, decreasing the critical temperature by the proximity effect. The critical temperature of the studied films varied from 56 to 302 mK. We have observed a significant change in the critical temperature of some films over time, which we propose to prevent by covering hafnium films with a thin layer of titanium.

Hafnium is a metal with rare properties, such as a low superconducting transition temperature slightly above 100 mK, which makes it attractive for a lot of applications, especially for design and fabrication of microcalorimeters with high energy resolution. In this paper we describe the results of fabrication and experimental investigation of superconducting properties of hafnium thin films in a dilution refrigerator. The considered Hf films, whose thickness is in the range from 60 to 115 nm, are deposited on substrates by electron beam evaporation. The combinations with thin layers of normal metals to decrease the critical temperature of superconducting hafnium films by proximity effect, are also considered. The critical temperature of the studied films varies from 56 to 302 mK. Also, significant increase of the critical temperature of some films over time was observed and investigated.

Cell is the important part of the terahertz (THz) spectrometer designed to study the chemical composition of multicomponent gas mixtures, since it is used for supporting the optimal pressure of the gaseous sample. However, the reflection of electromagnetic waves from the cell windows leads to standing-wave interference, which can distort the measured spectrum. Mathematical modeling of the impact of the interference on the measured spectrum was carried out in the paper. The cell was treated as a Fabry-Perot cavity with infinite flat dielectric mirrors. Diffraction of electromagnetic waves, as well as the frequency dependences of the source power and the detector sensitivity, was taken out of the scope of the considered model. The two effects of the interference were described. The interference not only determined the slow frequency dependence of the cell transmission spectrum, but also affected the profile of the gas absorption lines reconstructed from the cell spectrum in accordance with the Bouguer-Lambert-Beer law. Both the processing of the measured spectrum and the setup calibration required for accurate quantitative measurements could be complicated by the effects. However, methods of modulation and non-stationary spectroscopy enabled to eliminate the first effect, they were possibly ineffective to eliminate the second one. Presumably, the detected distortion of the contour of the absorption lines was caused by a shift in the interference pattern and, accordingly, a change in the reflection coefficient of the cell due to the anomalous dispersion of the sample. The correlation of the distortions with the derivatives of the transmission spectrum of the empty cell was revealed. The obtained results could be used to develop algorithms for calibrating the measuring setup and processing experimental data.

Here, we experimentally test the applicability of an aluminium Josephson junction of a few micrometers size as a single photon counter in the microwave frequency range. We have measured the switching from the superconducting to the resistive state through the absorption of 10 GHz photons. The dependence of the switching probability on the signal power suggests that the switching is initiated by the simultaneous absorption of three and more photons, with a dark count time above 0.01 s.

The major task of detecting axions or axion-like particles has two challenges. On the one hand, the ultimate sensitivity is required, down to the energy of a single microwave photon of the yoctojoule range. On the other hand, since the detected events are supposed to be rare, the dark count rate of the detector must be extremely low. We show that this trade-off can be approached due to the peculiar switching dynamics of an underdamped Josephson junction in the phase diffusion regime. The detection of a few photons’ energy at 10 GHz with dark count time above 10 s and the efficiency close to unity was demonstrated. Further enhancements require a detailed investigation of the junction switching dynamics.

The possibilities of using high-resolution terahertz spectroscopy for studying the composition of vapors of energy materials during their thermal decomposition were investigated. A high resolution nonstationary spectrometer for gas analysis based on the phase-shift of 115-178 GHz radiation acting on gas and a system heating the measuring cell and the reaction volume were developed and implemented. Possible mechanisms of thermal decomposition were found for four substances (ammonium nitrate, pentaerythritetetranitrate, octogen, triaminotrinitrobenzene) and sets of substances appearing during their thermolysis were determined experimentally. The results obtained show that high-resolution spectroscopy operating on nonstationary effects is a promising technique for qualitative analysis of multicomponent gas mixtures of the thermal decomposition products of explosives, including the appearance of products at different stages of sample heating. Besides the developed method can be used for the analysis of gas mixtures (gases, vapors, natural, and thermal decomposition products) of various origins for many applications (biology, medicine, agricultural applications).