The optical gain parameters in the six heavily doped AlxGa1 – xN:Si structures with x = 0.56, 0.62, 0.65, 0.68, 0.74, were experimentally studied at room temperature. Under optical excitation by pulsed radiation with λ = 266 nm, the mechanisms of stimulated emission of radiative recombination of nonequilibrium charge carriers, leading to the appearance of broadband radiation in the wide range (350–650 nm) of the spectrum with a high luminescence quantum yield are studied. High optical gain (>103 cm–1) are realized due to the good optical quality of the structures, large donor-acceptor recombination cross sections ( 10–15 cm2) and the high density (up to 1020 cm–3) of radiative recombination centers.

The experimental study of the laser on RM 4p2P3/2∘ - 3d2D5/2 (λ=854.2nm) and 4p2P1/2∘ - 3d2D3/2 (λ=866.2nm) transitions in a singly ionized calcium with active medium volume of 97 cm3 has been carried out. Excitation was performed with the periodic bursts containing 200 pulses each. It is shown that the laser pulse energy enters the steady-state mode during the burst. When the frequency of pulses inside the burst equaled to 90 kHz the steady-state value of the laser energy was 59 mJ, which corresponds to the average output power of 5.3 W. The measured power ratio between lines with λ=854.2nm and λ = 866.2 nm under optimum conditions amounted to 1.7, with radiation pulse duration of 20 ns. Experimental results for lasers on atom RM-transitions operating at pulse repetition frequency f≥100 kHz are reviewed. It is demonstrated that at such f values the energy characteristics of the Ca+ laser are comparable with those of lasers on atom RM transitions of other metals. An analysis of the mechanisms preventing further increase in the average output power when the pulse repetition frequency is increased above 100 kHz is presented.

The characteristics of barrier gas discharge in helium at atmospheric pressure are investigated when excited by pulses with voltage rise fronts of 3–10 ns and a pulse repetition rate of 5–100 kHz. The volumetric mode of the pulse current up to 80 A with a peak power of up to 1.5 MW and a specific power supply of an average power of up to 250 W cm−3 is realized. An increase in the steepness of the excitation pulses has little effect on the discharge current value but allows to maintain the volumetric nature of the current flow to the higher operating voltages. It is demonstrated that the maximum discharge current is restricted by an increase in ionization with an increase in the electron current from the cathode due to the ion–electron emission and charging of the dielectric surface, which increases the floating potential of the cathode surface relative to plasma.

The results of the investigation of the breakdown characteristics of the planar “open” discharge and open discharge with the generation of counter-propagating electron beams under excitation by pulses with nanosecond rise fronts are presented. The amplitude parameters of current and voltage and temporal characteristics of breakdown in helium, neon, and argon were measured. It is demonstrated that the breakdown in the open discharge is characterized by considerably larger electric field strengths at the same development delays as in the avalanche discharge. A similarity criterion based on the photoemission mechanism of electron generation, according to which the discharge development delay is inversely proportional to the squared working gas pressure, is obtained.

The abnormal discharge (AD) in pure helium and in helium containing molecular impurities was investigated. The obtained results were compared with the parameters of wide-aperture AD and different variants of ‘open’ discharge. It was shown that in all of the investigated types of discharges the current–voltage characteristics (CVCs) and, correspondingly, the emission properties of cold cathodes are determined mainly not by their material, but by the doping of cathodes with atoms of working gases and the purity of experimental conditions. With the impurity content less than 10 −4 % of the helium atom concentration, the CVCs begin to acquire S-shaped form, which is associated with a change in the electron emission mechanism. It was shown that the diversity of the CVCs is caused by uncertainty in the values of the secondary electron emission coefficients γ and the electron multiplication coefficient α in the cathode layer at reduced electric field strength E / N > 10 3 Td. The reproducibility of CVCs and, correspondingly, emission properties of cathodes can be ensured by high purity of the working gas and by maintenance of the cathode doping only by the working gas atoms.

Room temperature broad-band stimulated emission with transverse optically pumping was demonstrated from heavily doped Al0.68Ga0.32N:Si structures with external selective and non-selective cavities. The Al0.68Ga0.3N:Si films with thickness 1.2 mu m were grown by molecular beam epitaxy on (0001) oriented sapphire substrates. Stimulated emission was observed in the continuous wavelength range from 400 to 650 nm under pulse optical pumping of the YAG:Nd3+ laser with a wavelength 266 nm, 10 Hz repetition rate and 8 ns pulse width. Low optical pumping threshold power of 5 kW/cm2 at 490 nm in the external non-selective cavity has been observed. The nature of stimulated emission has been studied by means time-resolved spectroscopy. This broad band stimulated emission in the visible region is attributed with two main recombination mechanisms: slow donor-acceptor pair and fast free electron-acceptor transitions. The relative contributions of these processes are experimentally measured at all wavelength range of stimulated emission. The optical gain coefficients of (0.1-17.3) x 103 cm-1 have been determined at pump power density from 12 to 1040 kW/cm2 by direct measurement the gain of a probe radiation in the Al0.68Ga0.32N:Si structures.

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.

The broadband stimulated emission in the spectral range λ=380-700 nm with the inhomogeneous broadening has been experimentally obtined in the heavily doped Al 0.68 Ga 0.32 N : 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/cm 2 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. Keywords: stimulated emission, heavily doped Al x Ga 1-x N structures, luminescence, optical gain, donor-acceptor recombination.

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.

We present the results of a study of the breakdown characteristics of a planar "open" discharge in helium when excited by pulses with nanosecond rising edge. 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. Keywords: nanosecond gas discharge, breakdown, delay time, similarity condition.

We present the results of experimental studies of the output parameters of the lasers with a volume of 0.1 dm3 at RM transitions in barium and calcium ions. For Ca+ laser an average power of 4.5 W at a pulse repetition frequency of 100 kHz was achieved in the burst operation mode. For Ba+ laser the obtained steady-state average output power in the burst-mode operation amounted to 74 mW at a pulse repetition frequency 40 kHz. Typical laser pulse duration at half-maximum equaled correspondingly 13 and 5 ns for Ca+and Ba+ lasers.

Experimental results of the laser operating on the barium ion self-terminating transition 6p(2)P(3/2)(o) - 5d(2)D(5/2) at lambda = 614.2 nm investigations are presented. Through a series of tests, we demonstrated a significant improvement of the output characteristics of this laser by employing (i) a novel high-voltage nanosecond switch capable to operate at high pulse repetition frequency (more than 50 kHz), and (ii) hydrogen addition to the active medium. Achieved steady-state average output power in the burst-mode operation amounted to 125 mW with laser pulse duration of asymptotic to 5 ns at half-maximum.

The paper presents the results of studies of open discharge breakdown characteristics at nanosecond supply pulse in helium, neon, argon working medium in a wide pressure range. It is shown that the open discharge exists in the range of p He = 20–100 Torr, p Ne = 1.5–25 Torr, p Ar = 0.5–3.7 Torr with used experimental conditions. With increasing pressure, the role of separate elementary processes increases which can lead to a change of the discharge form to a presumably avalanche or streamer discharge. However, in this case, due to the photoemissive nature of the open discharge initiation, the similarity law Ep = f ( pι ) does not coincide with that for a nanosecond avalanche discharge.

Investigations of the operating parameters of a plasma-cathode switch based on a capillary discharge in helium and neon in the burst mode are presented. An increase in the efficiency of the switch is demonstrated when an additional preionization pulse is applied at a low pulse repetition frequency (5 kHz). The compression ratio of voltage pulses more than 300 is achieved at a pulse repetition frequencies less than 40 kHz.

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

Investigations of the operating characteristics of plasma switches based on the open discharge with the counter-propagating electron beams in helium, nitrogen, oxygen, and also in their mixtures have been carried out. In spite of the differences in the mechanisms of discharge burning for various conditions, which leads to the differences in switching characteristics, devices with switching times of 0.28–1.8 ns for design without a drift space and 1–2.5 ns with it are implemented. Even at a moderate voltage U ∼ 10 kV the obtained switching efficiency is in the range of 76%–95%, which exceeds values for the other gas-discharge devices, operating at high pulse repetition rate with ∼1 ns pulse leading front.

The pulse lasing in the broadband spectral range 420-590 nm was obtained from two squeezed together heavily Si doped Al0.74Ga0.26N/AlN/Al2O3 structures with external cavity under pump radiation with lambda(p) = 266 nm wavelength. These structures were grown by molecular beam epitaxy on (0001) oriented thick sapphire substrates. Stimulated emission at room temperature was observed with optical pumping thresholds 50 kW/cm(2) in the semiconfocal cavity. The linear transverse-electric polarization dominates in the output emission. The optical gain coefficients values of (0.12-6) x 10(3) cm(-1) for Al0.74Ga0.26N:Si films with inhomogeneous luminescence broadening were measured at 10-600 kW/cm(2) pump power density radiation with 266 nm wavelength, 8 ns pulse duration and 10 Hz repetition rate.

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 results of investigation of the current-voltage characteristics (CVCs) and electron beam generation efficiency in continuous discharges in helium, its mixtures with oxygen and nitrogen, as well as in pure oxygen and helium are presented. Peculiarities of CVCs are singled out and interpreted in terms of a changed role of the principal emission mechanisms with an increase in the voltage. It is shown that a high efficiency of the electron beam generation of more than 80% can be achieved in glow discharges in helium, oxygen, and nitrogen. In helium, it is provided by the predominating photoemission, while in oxygen and nitrogen and their mixtures with helium – mainly by the kinetic emission under the impact of fast heavy particles.

The results of investigation of a new type of switch (eptron), which expands the opportunities of voltage waveform tailoring for low temperature plasma applications, are presented. This switch consists of the device with counter-propagating electron beams (kivotron), which acts as a plasma cathode, and capillary integrated with the kivotron into a single device. The main advantage of a discharge in a capillary is various mechanisms of charge neutralization at different plasma densities. At a low density (10(10)-10(11)) cm(-3), free transport of electrons to the walls of the capillary occurs, due to which a large delay in the development of the discharge is realized. At a high plasma density, due to Debye screening, a rapid charges multiplication occurs and fast switching is realized. Under optimal conditions corresponding to the maximum value of the Townsend multiplication coefficient, a switching time less than similar to 1 ns is achieved. The comparative characteristics of the kivotron and eptron due to different mechanisms of subnanosecond switching are considered. The kivotron has a much lower inductance, which allows it to receive currents of tens of kiloamperes. Eptron operates more efficiently with a small characteristic size of the capillary, preferably a few tens of millimetres square. As a result, plasma recombination in the capillary in the eptron in the interpulse interval is much faster than in the kivotron, which allows operating at pulse repetition frequency above 100 kHz and the operating voltage of tens of kilovolts. The subnanosecond switching time in the eptron is realized at currents up to similar to 1 kA. Nevertheless, eptron provides new opportunities of voltage waveform tailoring, specifically for pulses generating with a subnanosecond leading edge. Particularly, it is demonstrated that lasing characteristics of BaII and HgII lasers on self-terminating transitions are significantly improved in comparison with conventional power supply.