Photoluminescence spectra of various samples made of polymethyl methacrylate (PMMA) induced by 222-nm-wavelength radiation of a KrCl excilamp with a bandwidth of ~ 2 nm and a narrow-band KrCl laser, as well as transmission spectra of these samples, have been investigated. It was found that the PMMA samples, according to their transmission spectra, can be divided into three characteristic groups with different short-wavelength transmission edges, which affect the photoluminescence spectra. It has been shown that the photoluminescence spectra of PMMA samples in the ultraviolet and visible regions depend on the power density of the exciting radiation.
The results of experimental studies of various generation modes of runaway electron beams (RAEBs) are presented. The main attention is paid to the mode when the RAEB with the highest amplitude are generated in air at atmospheric pressure. Other modes are discussed too: the most implemented and often mentioned by other authors generation mode as well as the mode when RAEB is generated after breakdown.
The study of exciton cathodoluminescence in diamond is not only scientific but also practical importance. Ultraviolet radiation at a wavelength of 235 nm can be used for disinfection, activation of surface reactions, photochemistry, and more. Thus, diamond is a promising material for creating a cathodoluminescent source of ultraviolet radiation. We have investigated the temperature dependences of the exciton cathodoluminescence spectra of single-crystal diamond in the temperature range from 80 to 400 K. The temperature dependences showed a characteristic increase in the intensity of exciton cathodoluminescence in the range 230-240 nm with increasing temperatures from 80 K to 150- 180 K. Further increase in temperature to room temperature (297 K) leads to a twofold decrease in the radiation intensity. With a further increase in temperature to 400 K, no change in the cathodoluminescence intensity was observed within the error
Cumulation effect of a beam of runaway electrons formed in a high-voltage nanosecond discharge in air at pressures of 3-105 Pa and discharge gap length d of 1 - 5 mm was studied. Optimal conditions of the effect in discharge gap with a tubular potential cathode and grounded flat anode was achieved at an air pressure of ~ 5 Pa and d of 2.7 mm. An electron beam current pulse was recorded behind a foil anode with high (up to ~ 80 ps) time resolution. It was found that, due to the cumulation effect, a through hole is formed in an aluminum foil 20 μm thick after 2-3 discharge pulses. The electron beam was found to register around the zone of maximum beam current density as well. As follows
The objective of the work is to study effect of the rise time of voltage pulses ranged from 15 ns to 1.5 μs on generation of runaway electron beams and X-ray radiation in nonuniform electric field. Three setups and different pressures of air, nitrogen, argon and helium were used. The experiments on the setup #1 have confirm that there are different regimes of generation of runaway electrons and X-ray emission when voltage pulses with a long front duration are used. When voltage pulse amplitude reached 150 kV at a pulse rise time of 1.5 μs, the new results was obtained on the setup #3. At this setup, a runaway electron beam was registered by a collector in argon, air, and nitrogen at pressures up to ≈ 12.5 kPa. When using helium, a supershort avalanches electron beam (SAEB) was obtained at a pressure of 100 kPa.
Optical absorption spectra in the temperature range of 85-300 K and IR absorption spectra at room temperature of four diamond samples were studied. All samples demonstrated the GR1 vibronic system of a neutral vacancy. The absorption coefficient at the zero-phonon line at 1.673 eV decreased by the power law in the temperature range of 120-230 K. Outside this temperature range, the absorption on the neutral vacancy did not practically changed. The value of the absorption coefficient at the neutral vacancy correlated well with the densities of nitrogen impurity-defective NV-, N2Vand N4V-complexes.
The cathodoluminescence spectra of nine diamond samples at temperatures of 82-295 K were investigated. According to the presence of the N3a vibronic system with the zero-phonon line at 2.68 eV in the luminescence spectra, six samples were identified as natural. By the presence in the luminescence spectra of the 2.56-eV vibronic system and the unstructured band at 2.54 eV, associated with nickel, two samples were identified as synthetic, grown at high pressure and high temperature. Due to exciton luminescence at 5.271 eV and the absence of any spectral features of impurity nature, one sample was identified as synthetic, grown by the chemical vapor deposition. Based on the data obtained, the technique for identifying of natural and synthetic diamonds has been proposed.
UV lasing is studied in nitrogen and the N2-SF6 mixture pumped by a volume discharge initiated by a runaway-electron
preionised diffuse discharge (REP DD) produced in an inhomogeneous electric field. It is shown, that lasing at a
wavelength of 337.1 nm is observed at pressures up to 2.5 atm without any preionisation source. At a pressure of 0.5 atm
with the use of blade electrodes and the N2 :SF6 =10:1 active medium of length ~6 cm, the output laser energy of ~2 mJ
was achieved for the pulse power of 0.55 MW. The REP DD pumping regime is compared with the regime of pumping
by a volume discharge produced by a preionisation source.
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