The gain characteristics of heavily doped AlxGa1-xN/AlN: Si structures with x = 0.65 and 0.74 under optical pumping by a pulsed Nd:YAG laser radiation with lambda= 266 nm have been experimentally studied at room temperature. The absolute values of the optical gains are (0.5–6)*10^3 сm-1 in the maximum of the luminescence spectrum at the excitation power density (8–600) kW/cm2. The obtained cross sections for the radiative and donor–acceptor recombination coincide with each other and exceed the 10^(-16) сm2.

The lasing characteristics of a copper vapour laser in a tube with forced heating, having a length of 50 cm and a diameter of 2 cm, excited by a train of pulses are investigated. Comparative studies of the frequency and energy characteristics of the laser are performed with a leading edge duration of the excitation pulse of ∼25 ns (when the capacitance discharges through a thyratron and a magnetic compression line) and ∼3 and 1 ns (using circuits with a high-speed switch – kivotron). It is shown that a decrease in the leading edge duration gives rise to an increase in the optimal pulse repetition rate up to ∼30 kHz, the generation efficiency up to 3.2 % and the generation power per unit length over 100 W m−1. The results obtained confirm the concept of limiting the frequency and energy characteristics of a copper vapour laser due to the insufficient rate of energy input into the plasma at high prepulse electron concentrations.

AbstractThe main features of a continuous open discharge used to generate electron beams in medium-pressure gases are discussed. I – V characteristics have been investigated, current and energy efficiencies have been measured, and conditions for obtaining a high (comparable with the anode geometric transparency) energy efficiency of beam generation in helium at a pressure of 10–30 Torr and its mixtures with oxygen have been established. Fundamental differences between the investigated and anomalous discharges have been found. In particular, a Z-shaped I – V characteristic has been obtained and attributed to the modification of the role of main electron emission mechanisms with increasing voltage.

Исследован спектр возбуждения ридберговских состояний атомов таллия с использованием коллимированного атомного пучка в двухступенчатой изотопически селективной лазерной схеме 6 2 P 1/2 → 6 2 D 3/2 → Tl * * в присутствии электрического поля с напряженностью до 1.5 kV/cm вблизи уровня 16F 5/2 .Экспериментально изучены индуцированные внешним электрическим полем дипольно запрещенные оптические переходы 6D 3/2 → 18D 3/2 и 6D 3/2 → 16G 7/2 .Получены значения для скалярных поляризуемостей (в ед.сm -1 /(kV/сm) 2 ): α 0 (16F 5/2 ) = 3.71 ± 0.3, α 0 (18D 3/2 ) = 11.70 ± 0.25 и α 0 (16G 7/2 ) = 44.1 ± 0.9, которые сравниваются с расчетными.Определены новые значения энергетических параметров для состояний 18D 3/2 и 16G 7/2 .

The main features of a continuous open discharge used to generate electron beams in medium-pressure gases are discussed. I–V characteristics have been investigated, current and energy efficiencies have been measured, and conditions for obtaining a high (comparable with the anode geometric transparency) energy efficiency of beam generation in helium at a pressure of 10–30 Torr and its mixtures with oxygen have been established. Fundamental differences between the investigated and anomalous discharges have been found. In particular, a Z-shaped I–V characteristic has been obtained and attributed to the modification of the role of main electron emission mechanisms with increasing voltage.

Представлены результаты исследования планарного открытого" разряда с генерацией встречных электронных пучков при высоком напряжении и значительных, вплоть до атмосферного, давлениях рабочего газа. Продемонстрирована возможность его функционирования в гелии при напряжении свыше 100 kV, при этом повышение рабочего напряжения не препятствует быстрому пробою c характерными временами коммутации ~1 ns. Особенностью этого типа разряда является существование области давлений газа, в которой наблюдается немонотонная зависимость времени задержки развития разряда от напряжения, связанная с конкуренцией эмиссионных процессов, приводящих к пробою. DOI: 10.21883/PJTF.2017.20.45148.16930

При оптической накачке импульсным лазерным излучением с lambda = 266 nm твердых растворов AlxGa1-xN/ AlN с x = 0.5 и 0.74, синтезированных методом молекулярно-лучевой эпитаксии, исследованы спектральные характеристики спонтанной и стимулированной люминесценции. Получены широкополосные спектры излучения с шириной ~ 260 THz для Al0.5Ga0.5N и ~ 360 THz для Al0.74Ga0.26N. Измеренные коэффициенты усиления на lambda~ 528 nm для Al0.5Ga0.5N равны g~ 70 cm-1, а для Al0.74Ga0.26N на lambda~ 468 nm g~ 20 cm-1.

The influence of a pre-pulse population of copper atom metastable states and their sub-population at a current pulse edge on the copper vapour laser pulse energy is studied under optimal temperature conditions. Experiments have been performed with active elements of a commercial laser having an internal diameter of a discharge channel of 14 and . It is found that at a pulse repetition frequency of , corresponding to a maximal output power, the reduction of the energy due to a residual population of metastable states is by an order of magnitude less than due to their sub-population at a current pulse edge. The modelling based on the experimental results obtained has shown that in the case of an active element with an internal diameter of , a decrease in the pulse leading edge from to does not reduce the laser pulse energy up to the repetition frequency of at an average output power of and efficiency of .

Lasing on self-terminating copper atom transitions is obtained for the first time by pumping the Ne-CuBr mixture by regular pulses and by a pulse train of low-energy electron beams formed in an 'open' discharge. In these regimes in a range of experimental conditions, a growth of power and radiation energy is demonstrated with an increase in the electron beam current and pulse repetition rate. In a double pulse excitation regime, the lasing energy is completely recovered in similar to 2.5 mu s. In a central zone of the active element where CuBr molecules are totally dissociated, the specific lasing energy of similar to 44 mu J cm(-3) is obtained at a physical efficiency of 8.5%.

We report an experimental study of the performance parameters of a gas discharge pumped thallium vapour laser operating on the 7s2S1/2 - 6p2P3/2o self-terminating transition at 535 nm. The switch we used, a TPI3-10k/25 cold-cathode thyratron, ensures a rise time of the load voltage pulse less than 15 ns. The laser output power is shown to increase in proportion to the energy stored in the discharge capacitor (up to the maximum voltage of the thyratron). The optimal pump pulse repetition rate for He(Ne)—Tl mixtures is ∼1.75 kHz. Even small hydrogen additions reduce the lasing energy and average output power. The addition of bismuth vapour increases the optimal pulse repetition rate (up to 3 kHz) and average output power. The factors responsible for the lower lasing efficiency in comparison with the copper vapour laser are analysed.

The quasi-continuous wide-aperture glow discharge in helium at pressures from 1.2 to 6.0 Torr is studied. It is found that electron beam generation efficiency η is higher than 96% in the pressure range 1.2–3.0 Torr at voltages from 1.0 to 2.6 kV. The maximum power was ≈ 0 kW at 6 Torr and a voltage across the discharge gap of 2.6 kV. Under these conditions, the beam generation efficiency is about 80%. The pressure and voltage dependences of main parameters of the discharge are explained from the standpoint of its photoemission nature.

Экспериментально исследованы энергии и квантовые дефекты ридберговских состояний nF5/2 (n = = 13–24) атома таллия, возбуждение которых осуществлялось из основного состояния 62P1/2 по двухступенчатой схеме через промежуточное состояние 62D3/2. Применением коллимированного атомного пучка, монохроматического излучения двух узкополосных перестраиваемых лазеров разрешены сверхтонкая и изотопическая структуры основного состояния атома таллия и определено энергетическое положение состояний nF5/2 с точностью 0.03 см-1, превышающей более чем на порядок точность, реализованную в предыдущих работах. Величина квантового дефекта nF5/2 не зависит от n в пределах точности измерений и равна = 1.0344 ± 0.0008. Значение ионизационного потенциала Ip = 49266.55 ± 0.03 см-1 получено для изотопа 205Tl с уровня 62P1/2 (F = 0). Измеренная в эксперименте относительно состояния F = 0 изотопа 205 энергия уровня 62D3/2 составила 36118.56 ± 0.02 см-1.

The energies and quantum defects of Rydberg states nF 5/2 ( n = 13–24) of the thallium atom have been studied experimentally. The Rydberg states were excited from the ground state 6 2 P 1/2 by the two-stage scheme through the intermediate state 6 2 D 3/2 . By using a collimated atomic beam and monochromatic radiation of two narrow-band tunable lasers, we have succeeded in resolving the hyperfine and isotopic structures of the ground state of the thallium atom and in determining the energy positions of the states nF 5/2 accurate to 0.03 cm −1 , which exceeds the accuracy achieved in the previous works by more than an order of magnitude. The quantum defect of nF 5/2 states is independent of n within the measurement accuracy and is equal to Δ = 1.0344 ± 0.0008. The ionization potential I p = 49266.55 ± 0.03 cm −1 has been found for the 205 Tl isotope from the level 6 2 P 1/2 ( F = 0). The energy of the 6 2 D 3/2 level measured experimentally relative to the state F = 0 of the 205 isotope amounted to 36118.56 ± 0.02 cm −1 .

A laser on the self-contained helium 2(1)P(1)(0) - 2(1)S(0) transition pumped by a pulsed electron beam generated in an open discharge is simulated and experimentally studied. Lasing without decreasing the pulse energy in a tube of diameter 31 mm was observed up to the pump pulse repetition rate of 10 kHz determined by the parameters of a power supply. Dynamics of the electric field in an accelerating gap and populations of the working levels of helium are calculated. The radiation power calculated in accordance with its radial distribution measured in the saturated amplification regime is 7.85 times higher than that in the lasing regime. The practical laser efficiency of 0.056% is achieved for the quantum efficiency of 0.7%.

Разработан импульсный лазерный источник перестраиваемого ультрафиолетового излучения с шириной линии <400 МГц, длительностью импульсов 9 нс, частотой повторения 11 кГц с накачкой лазером на парах меди. На длине волны 276 нм средняя выходная мощность составила 1.5 Вт. Система, предназначенная для лазерного разделения изотопов, содержит задающий генератор на основе лазера на красителе, два усилительных каскада со средней выходной мощностью излучения 4.5 Вт на длине волны 553 нм и удвоитель частоты излучения на кристалле ВВО. Задающий лазер выполнен по схеме с дифракционной решеткой, расположенной под углом, близким к скользящему, с призменным расширителем пучка и воздушным герметизированным эталоном Фабри–Перо. Долговременная стабильность частоты выходного излучения составила 10 МГц/ч.

The collisions of metastable Pb(6p 2 1 D 2) atoms with various molecules were studied by the diagnostics of radiation from a hollow cathode lamp and a laser on lead vapor. Experiments were performed for a gas flow of lead atoms with argon. The Pb(6p 2 1 D 2) states were excited in a gas discharge in the presence of reagent gas molecules. The absolute rate constants for the quenching and chemical reactions of lead atoms in the ground and excited states were determined. The quantum efficiency of chemical reactions was close to one for the N2O, CH2Cl2, SF6, and CuBr molecules. Long-lived chemical compounds were formed in these reactions.

The broadening of a two-photon resonance is studied experimentally at the 4s1S0−6s3S1 transition in a zinc atom upon absorption of two waves with a small detuning from an intermediate state in collisions with CO2, CO, and NO molecules. The measured absolute values of broadening cross sections greatly exceed gas-kinetic cross sections and are (9.4±2.4, 6.5±1.6, and 3.9±1.0)×10− 14cm2 for CO2, CO, and NO, respectively. Anomalously large rate constants and cross sections obtained in experiments are explained by the efficient resonance quenching of the excited states of zinc atoms in collisions with molecules accompanied by transfer of the energy of excited atoms to vibrational-rotational degrees of freedom of molecules.