Исследованы характеристики барьерного газового разряда в гелии при атмосферном давлении при возбуждении импульсами с фронтами нарастания напряжения 2.5-10 нс и частотой следования импульсов 5-100 кГц. В объемном режиме получен импульсный ток до 80 А с пиковой мощностью до 1.5 МВт и удельной мощностью до 250 Вт/см3. Увеличение крутизны импульсов возбуждения незначительно влияет на величину тока разряда, но позволяет сохранить объемный характер протекания тока до более высоких рабочих напряжений. Показано, что максимальный ток разряда ограничивается накоплением заряда на поверхности диэлектрика и, тем самым, увеличением её плавающего потенциала, что приводит к уменьшению разности потенциала относительно квазинейтральной плазмы. Показано, что увеличение разрядного промежутка и увеличение напряжения вызывает переход от однородного объемного протекания тока к шнурованию.

В эксперименте и численном моделировании проводится сравнение интенсивности взаимодействия гелиевой холодной плазменной струи (ХПС) с диэлектрической поверхностью и с кожей животных. ХПС при атмосферном давлении генерируется синусоидальным или положительным импульсным напряжением с различной длительностью импульса в оптимальных режимах. Эффект воздействия оценивается на основе измеренных и рассчитанных токов, интенсивностей линий в спектре ХПС и температурных полей. Измеренные характеристики ХПС показывают, что импульсный характер возбуждения ХПС является предпочтительным по сравнению с синусоидальным режимом. Варьирование длительности импульсов периодического импульсного напряжения позволяет получить максимальные ток и напряженность электрического поля у поверхности в рамках допустимой температуры в зоне контакта ХПС с кожей мышей (<42°C). Показано, что результаты исследования ХПС полученные в физических экспериментах с использованием диэлектрической пластины применимы для воздействия на мышей-опухоленосителей.

Comparative studies of the generation of a cold plasma jet atmospheric pressure in helium excited by a sinusoidal voltage with different methods of its initiation have been carried out. The frequency and temperature ranges of the plasma jet, acceptable for exposure to biological objects, were determined.

Низкотемпературные плазменные струи при атмосферном давлении, генерируемые синусоидальным и положительным импульсным напряжением, по-разному взаимодействуют с обрабатываемой поверхностью. В эксперименте и в численном моделировании сравниваются режимы работы струи гелиевой плазмы для этих типов рабочих напряжений. Ток разряда на обрабатываемой поверхности с течением времени, и нагрев поверхности изучены для различных параметров разряда, допустимых для противораковой терапии. Для повышения эффективности плазменной струи анализируется интенсивность спектра излучения. Нагрев поверхности контролируется для того, чтобы удовлетворить условиям безопасного плазменного воздействия на биологические объекты. Обсуждается влияние длительности импульса напряжения на интенсивность взаимодействия плазмы с поверхностью. Результаты воздействия на раковые клетки A549 и MCF-7 демонстрируют высокую эффективность холодной плазменной струи, генерируемой в оптимальных режимах.

The generation of a cold plasma jet of atmospheric pressure in helium by unipolar positive pulses excitation at a voltage of 2–6 kV and the impact on a dielectric target made of aluminum oxide has been studied. It is shown that the main parameter influencing the regular nature of the streamer breakdown is the pulse duration, and the achievable parameters of cold plasma impact on the target identical to those for sinusoidal excitation.

The broadband stimulated emission in the spectral range λ = 380−700 nm with the inhomogeneous broadening has been experimentally obtined in the heavily doped Al0.68Ga0.32N : Si structures grown by molecular beam epitaxy. The behavior of the intensities and spectra of stimulated emission from the edge of the active element with transverse pulsed pumping by radiation with λ = 266 nm, measured at room temperature, demonstrate the threshold behavior and optical gain. For stimulated emission with a maximum at λ = 500 nm, the minimum threshold pump power density was 6.5 kW/cm2 for excited region length of 1.5 mm. The parameters and contributions of the two main processes e − A and D − A of radiative recombination in the excited structures for stimulated emission and optical gain are studied.

We present the results of a study of the breakdown characteristics of a planar "open" discharge in helium when excited by pulses with nanosecond rise fronts. It is demonstrated that the development of the discharge is characterized by considerably larger values of the reduced electric field strength than in the avalanche discharge. A similarity criterion was obtained for discharges with a predominance of the photoemission mechanism of electron generation, according to which the rate of discharge development is proportional to the square of the working gas pressure.

Comparative studies of generation of cold plasma jet of atmospheric pressure in helium when excited by sinusoidal voltage and unipolar positive pulses at 2-6 kV for medical applications have been conducted. It is shown that the achieved parameters are identical, but the absence of the effect of frequency self-organization of streamer breakdown leading to irregularity in streamer propagation under pulse excitation makes it preferable in biophysical experiments. A limiting factor for plasma jet exposure is the achievable target temperature, which can be reduced by limiting the duration of the current.

Time-resolved luminescence and stimulated emission intensities has been experimentally investigated in heavily doped Al0.65Ga0.35N and Al0.74Ga0.26N structures under pulsed optical excitation. These results showed that the time decay of the luminescence and stimulated emission intensities for various wavelengths of the emitted spectrum and optical pumping intensities consisting of at least the fast and the slow components. Fast components with exponential time decay are responsible for the radiative recombination of nonequilibrium electrons on deep acceptors, while slow ones are responsible for the recombination of donor-acceptor pairs

Comparative studies of the switching characteristics of devices based on an open discharge - kivotrons in molecular gases (nitrogen and oxygen), as well as their mixtures with helium - have been carried out. The choice of nitrogen and oxygen is due to the fact that the emission coefficients of electrons under the action of their heavy particles are much higher than for helium. It is shown that for this case, as well as with the predominance of the photoelectronic emission mechanism in helium, it is also possible to create fast switches. Their advantage is significantly lower requirements for the cleanliness of the working environment.

The spectrum of excitation of Rydberg states of thallium atoms has been investigated using a collimated atomic beam in a two-step isotope selective laser scheme 62P1/2 → 62D3/2 → Tl** in the presence of an electric field with a strength of up to 1.5 kV/cm near the level 16F5/2. The optical transitions 6D3/2 → 18D3/2 and 6D3/2 → 16G7/2, which were induced by an external electric field and dipole-forbidden, have been studied experimentally. The values for the scalar polarizabilities (in units сm–1/(kV/сm)2) α0(16F5/2) = 3.71 ± 0.3, α0(18D3/2) = 11.70 ± 0.25, and α0(16G7/2) = 44.1 ± 0.9, which are compared with the calculated one, have been obtained. The new values of energy parameters for the states 18D3/2 and 16G7/2 have been determined.

Spectral, temporal, and polarisation characteristics of luminescence of heavily doped AlxGa1-xN films on a sapphire substrate are studied under pulsed pumping at the wavelength lambda = 266 m. Spectra of spontaneous emission related to donor - acceptor transitions are inhomogeneously broadened with the FWHM of above 0.5 eV and cover the entire visible range. Spectra of radiation emitted from an edge of investigated structure comprise several narrow-band equidistant components, each of them being split to TE and TM modes with mutually orthogonal polarisations. This is related to plane waves propagating inside a plane waveguide along a zigzag path in the conditions of total internal reflection from waveguide surfaces. The optical gains measured for Al0.5Ga0.5N/AlN at lambda approximate to 510 nm, Al0.74Ga0.26N/AlN at lambda approximate to 468 nm, and AlN/Al0.6Ga0.4N/AlN/Al2O3 at lambda approximate to 480 nm were, respectively, similar to 70, 20, and 44 cm(-1). The luminescence quantum efficiencies measured for Al0.74Ga0.26N, Al0.65Ga0.35N, and Al0.5Ga0.5N films are, respectively, 0.79, 0.49, and 0.14; the transition cross sections calculated at emission band centres are similar to 10(-18) cm(2).

A new type of switch based on a photoelectron open discharge is studied. The switch can generate high-voltage pulses with a subnanosecond leading edge. The coaxial and planar designs of the switch are studied. The feasibility of switching currents reaching several tens of kiloamperes with a switching time of less than 0.4 ns at a voltage of up to 20 kV, a pulse repetition rate of up to 100 kHz, and an efficiency of no less than 0.9 is demonstrated.

The lasing characteristics of a copper vapour laser are investigated in the regime of a pulse train excited in the internal-heating tube with the diameter of and length of . Two power supply schemes are compared: a conventional scheme with a storage capacitor discharged through a thyratron connected to a peaking capacitor and the scheme in which the peaking capacitor is connected to the laser active element through a kivotron – a fast switch based on the ‘open discharge’ with a turn-on time of less than . It is shown that in the considered range of the pulse repetition rates in the first case we deal with a typical energy dependence on frequency having a maximum near . In the second case, the lasing energy is frequency-independent; hence, the average power in this range is proportional to . The results obtained are explained by the neutralised influence of the initial electron concentration on energy characteristics of the copper vapour laser.

An open hollow-cathode discharge, generating an electron beam, is implemented in a cell with an active volume of 6.2 L. An electron-beam current of 3.4 A at an average power of 2.5 kW is obtained in helium in the quasi-cw regime at an anode voltage of 1.5 kV. Lasing in a He-Xe mixture on the 5d[3/2](1)(0)-6p[3/2](1) transition in xenon at the wavelength lambda = 2.026 mu m under electron-beam excitation is investigated. The optimal component ratio in the He : Xe mixture is 99.5 : 0.5 (p(He) = 4-8 Torr). The lasing power linearly increases with increasing the electron-beam power. It is shown that the discharge of this type can be used as an electron-beam source for exciting gaseous active media.

Laser on a self-contained transition of a helium atom is studied under excitation of the helium mixture with molecular gases by single long-duration (up to 700ns) or double nanosecond pulses. In He — H2O and He — NH3 mixtures, no limitations were found on the pulse repetition rate and the laser pulse duration obtained was equal to that of the pump pulse.

A comparative analysis of the techniques of laser isotope separation in monatomic vapors is presented. The restraints inherent in the conventional isotope separation technique AVLIS (atomic vapor laser isotope separation) are discussed as applied to the large-scale production of various isotopes. The requirements that should be met by the chemical reactions are formulated for the use of these reactions in isotope separation. The photochemical technique was shown to be quite competitive with the AVLIS.