In this work, we propose a simple method for generating Bessel vortex beams in the subterahertz (subTHz) range with the orbital angular momentum with l = 1 based on reflecting metal diffractive optical elements with a continuous helical microrelief. The elements are fabricated by micromilling in a polished duralumin substrate and by tin casting, and tested using a backward wave oscillator (wavelength λ = 855 µm). When using the micromilled element, Bessel vortex beams are shown to be generated and retain a Bessel intensity profile at a distance of 20–50 mm from the reflecting element, which is in good agreement with the results of numerical simulation. An experimental estimate of the energy efficiency of this element is 63%. When using elements made by tin casting, the vortex beams are generated with a distorted profile due to the presence of residual deformations of tin, which has plasticity. Due to their high conductivity, metallic reflecting elements can be used with high power density sub-THz radiation sources such as free electron lasers and gyrotrons.

Long-term ground-based lidar observations are important in estimating the contribution of different sources (mostly volcanic eruptions and wildfires) to aerosol loading of the atmosphere and in developing and improving various climate models. In this paper, we carefully analyse aerosol scattering ratio profiles and aerosol layers, observed with 532-nm lidar measurements at the Siberian Lidar Station in Tomsk (56.48 degrees N, 85.05 degrees E) over the period 2018-2022, and identify the layers' potential sources. To compare aerosol loading over Tomsk for the last five years (2018-2022) with that for previous years, we also present and discuss time series of integrated aerosol backscatter coefficient (IABC) for three altitude ranges. The first range (15-30 km) reveals the pure stratospheric aerosol loading provided by volcanic eruptions, the second range (11-15 km) is responsible mainly for aftereffects of wildfire smoke plumes, and the third one (11-30 km) demonstrates aerosol contribution from both sources. In particular, we found for the period 2001-2022 that the annual average IABC reached its maximal values of 2.91 x 10-4 sr-1 (15-30 km) and 8.21 x 10-4 sr-1 (11-30 km) in 2022 due to the Hunga Tonga-Hunga Ha'apai volcanic eruption. The period 2020-2022 exhibited a significant increase in the relative aerosol content at altitudes of 11-15 km in the total aerosol loading at 11-30 km over Tomsk from 54.4% in 2020 to 64.8% in 2022, which indicates a shift of the main part of aerosol loading to altitudes of 11-15 km due to the increased wildfire activity in North America and north-eastern Asia. The Arctic polar vortex is also revealed to distort the real aerosol vertical distribution over Tomsk by replacing it with the aerosol distribution inside the vortex on measurement days when the vortex is over the lidar site.

The results of observation of Ramsey oscillations in germanium doped with arsenic donors detected by photothermal ionization of Coulomb centers are presented. To excite quantum coherent superpositions of the states at the transition 1 s (A 1 )–2 p 0 the Novosibirsk free electron laser radiation was used. The results are analyzed using a theoretical model using several key parameters of the experiment.

Currently, the terahertz-frequency range, which is on the border of the microwave and optical ranges, is being intensively utilized. One of the widely used materials in terahertz optics is indium antimonide (InSb), the plasma frequency of which depends on the degree of doping, temperature, and surface illumination. The possibility of generating surface plasmon polaritons, a type of surface electromagnetic waves, on the surface of an InSb sample using the attenuated-total-reflection method (ATR) (Otto scheme) is discussed. Using the scattering-matrix formalism, the conditions for the highest efficiency of the excitation of surface plasmon polaritons are established. If terahertz radiation with a frequency ω slightly less than ωp is used for this, the propagation length of such plasmons and the depth of their field penetration into the environment (air) are comparable to the radiation wavelength. It is possible to achieve surface plasmon resonance in the form of a sharp decrease in the intensity of monochromatic radiation reflected from the base of the ATR prism with a change in the angle of incidence and the size of the air gap. Test experiments were performed to observe the surface plasmon resonance on an InSb wafer using a high-resistance silicon prism and monochromatic radiation (λ = 141 μm) from the Novosibirsk free electron laser. The dependence of the resonant dip on the size of the air gap separating the prism from the sample surface is studied, and its optimal (in the case of resonance) value is established for semiconductors with a plasma frequency in the terahertz range.

Sensors based on surface plasmon resonance excited in the scheme of attenuated total reflection (ATR) on thin metal films have undergone a revolution in the visible frequency range. It is possible to study very weak interactions, up to single molecules, using these sensors. Such an approach, which has already become classical, cannot be implemented in the terahertz-frequency range. Terahertz waves barely penetrate metals due to their high dielectric constant, which makes it difficult to maintain resonance at the metal–dielectric interface. One way to overcome this problem is to modify the metal surface with a structure with a characteristic size much smaller than the radiation wavelength. The structured region of the metal behaves as an effective layer of the medium, the permittivity of which is a function of the response of the dielectric and the metal. On these structures, spoof-surface plasmon resonances, which are similar in properties to surface plasmon resonances in the visible range, can be excited. By combining spoof-surface plasmon resonance and attenuated total reflection, it is possible to implement a sensor that, in the future, will make it possible to detect the smallest concentrations and observe small changes in the boundary dielectric medium in the terahertz-frequency range. The excitation of a spoof-surface plasmon resonance is studied using the method of attenuated total reflection on a flat one-dimensional subwavelength grating with gold sputtering in the Otto scheme. For the first time, the angular reflection spectra are measured according to this scheme using monochromatic terahertz radiation from the Novosibirsk free-electron laser (the wavelength is 141 μm). The plasmon resonances observed in the spectra are consistent with the simulation results using COMSOL Multiphysics.

A problem of optimizing the subwavelength microrelief of a binary cylindrical transmissive diffractive lens (DL) with a 300-mm focal length for a wavelength of λ=141 μm was considered. High-resistivity silicon was chosen as the DL substrate material. The angle of incidence of the illuminating beam was taken to be π/6. The optimization parameters were the height of the DL profile and the fill factor of the groove. The main goal of optimizing the design was to increase the diffraction efficiency of the lens. The DL diffraction efficiency was calculated using a Fourier mod method. The DL was fabricated by plasma-chemical etching (Bosch process) of the surface of a silicon substrate. The diffraction efficiency of the calculated lens was estimated to be 70%. However, a full-scale experiment showed the real efficiency to be much lower. These differences are related to both errors in the manufacturing process of the DL and non-ideal thickness parameters of the silicon wafers.

Acoustic signals coming from the human head during mental activity are experimentally studied. Acoustic signals that differ from the signals during relaxation are revealed. Calculation of the multiplication table in the mind is used as mental activity. It is shown that the differences are due to a variation in the breathing pattern. It is also shown that the most informative signals related to respiration are observed from the crown region (at a point close to Cz used in encephalography) and the signals related to pulse activity are observed from the temple region (at point T-3).

The optical scheme and technical characteristics of terahertz planar Michelson interferometer based on surface plasmons are presented. A technique for determination of the complex index of refraction of surface plasmons ( ñ_s = n_s + iκ_s ) from interferograms is described. The paper presents the results of test measurements on flat surfaces with gold sputtering coated by ZnS layers 0 to 3 μm thick with application of the high-power coherent radiation from the Novosibirsk free electron laser at the wavelength λ 0 = 141 μm. From the measurement results, the value of the effective permittivity of the sputtered gold surface was found, which turned out to be an order of magnitude lower than that of crystalline gold. Analysis of the energy losses in the plasmonic interferometer made it possible to estimate its dynamic range (10 6 –10 8 in terms of radiation power) required for measurements on samples with different ñ_s . Ways to increase the signal-to-noise ratio via optimization of the elements of the optical scheme and detector have also been proposed.

This paper describes stations, both existing and under development, for the diagnostics of beam parameters of the 3rd stage of the Novosibirsk free electron laser (FEL). A modification of the method for measuring electron energy spread using the spectrum of spontaneous undulator radiation under the operating conditions of the Novosibirsk FEL is presented.

Ramsey oscillations have been observed in germanium doped with shallow impurities exposed to terahertz pulses from the NovoFEL facility involving free-electron lasers in experiments performed using the standard method with the action of a sequence of two optical pulses at the frequency close to the frequency of the 1 s ( A 1 ) → 2 p 0 impurity transition. The coherent state of the ensemble of donors has been detected by measuring the photocurrent caused by the thermal ejection of electrons from the 2 p 0 state to the conduction band. The revealed effect is quite stable under experimental conditions, in particular, to the temperature regime, which allows the further improvement in artificial systems based on shallow donors in germanium.

Comparative studies of characteristics of Bessel and "perfect" vortex beams with a topological charge 9, created using a binary silicon axicon and a "holographic" diamond axicon with continu-ous profile at a wavelength of 141 μm, are carried out. Beams with linear and radial polarization are investigated. An example of the use of a perfect radially polarized beam for the excitation of vortex plasmon-polaritons on a cylindrical conductor is given.

The effect of collisional line broadening on the accuracy of tropospheric (0–11 km) temperature measurements with pure rotational Raman (PPR) lidars at their absolute calibration by spectroscopic parameters was estimated via numerical simulation. The simulation was performed for five sets of spectral filters (SF) with different passbands in a lidar spectral selection unit and an outgoing laser signal wavelength of 355 nm. It is shown that the unavoidable absolute calibration error can reach values from 0.14 to 0.44 K (depending on a SF set) when ignoring the N2 and O2 PRR line broadening. The line broadening can be neglected if only one PRR line is extracted in each of the two lidar channels (for example, using a Fabry–Perot interferometer).

В данной работе представляются первые экспериментальные результаты по измерению реальной и мнимой частей показателя преломления ППП с помощью плазмонного интерферометра Майкельсона с использованием монохроматического перестраиваемого терагерцового Новосибирского лазера на свободных электронах (ЛСЭ). Это стало возможным благодаря предшествующим экспериментальным исследованиям по генерации и распространению ППП, их отражению плоскими зеркалами, делению с помощью тонких диэлектрических пленок. В качестве образцов использовались полированные стеклянные пластины с непрозрачным золотым напылением, покрытые слоем ZnS толщиной от 90 до 1000 нм. Точность измерения реальной части показателя преломления ППП зависела от толщины диэлектрического покрытия и стабильности работы ЛСЭ, достигая 3∙10-4 RIU.