Contrast enhancement in an electron-beam-excited wide-aperture XeCl laser

The possibility of increasing the contrast in the problem of the generation of petawatt radiation when the energy is released by a femtosecond laser pulse in the presence of a prepulse that passes through the medium of an electron-beam-excited wide-aperture amplifier prior to the main pulse is considered. It is demonstrated that such an approach does not lead to a significant increase in the contrast.     

Long pulse electron beam excited XeF laser

Long pulse operation of the XeF laser has been achieved with a short gain length and medium intensity electron beam excitation for both Ar/Xe/NF₃ and Ne/Xe/NF₃ mixtures. Use of Ne as diluant strongly lower the threshold for lasing and give an important increase in extracted power. For a total mixture pressure of 2 atm about 6 mJ of 3500 Å radiation was obtained in a 400 ns fwhm pulse limited only by e-beam pulse length.     

Electron beamexcitation of wide-aperture XeCl lasers

This paper presents the results of studies aimed at seeking efficient modes of electron beam excitation ofXeCl lasers with an active volume of some tens of liters. It has been shown that a lasing efficiency of about 4% is realized at an excitation pulse duration of 300 ns with a power of 200–400 kW/cm³. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 29–33, April, 2000.     

On localized structures of radiation in a wide-aperture laser with a transverse inhomogeneity

The analysis of the stability of the generationless regime in a laser with a smooth transverse inhomogeneity of the resonator length is performed. Localized structures of radiation are considered that are possible in this laser when the nonlinearity of the gain and of the refractive index of the medium is taken into account.     

Formation of highly coherent radiation in a wide-aperture exciplex laser

The results of experimental investigations into the feasibility of improving the spatial and temporal coherence of the radiation of aXeCl laser with a 16×12 cm output aperture and a pulse output energy up to 150 J are given. It is shown that in the injection-locked mode, 90% of the output energy can be emitted in a narrow spectral line. An unstable resonator with mirrors small in size and generalized parameters g_i>1 allows a near-diffraction-limited beam divergence to be obtained. Institute of High-Current Electronics of the Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 53–56, August, 1999.     

100 MW, 248.4 nm,KrF laser excited by an electron beam

Laser oscillations have been observed at 248.4 nm from excited KrF molecules. The excited KrF molecules were produced by injecting an intense electron beam into mixtures of Ar, Kr and F₂. A peak power of 1.15 × 10⁸ W with a total energy of 5.6 J has been observed. Up to 3% of the deposited e-beam energy was converted to laser-energy.     

自由电子激光器谐振腔内电子束和激光脉冲的时间同步

研究自由电子激光器谐振腔内电子束和辐射的时间同步问题.这是激光器谐振腔设计中的一个重要问题.本文讨论了腔内布儒斯特窗片对光路的影响.研制出由微机控制谐振腔的精密微调装置,扫描范围为±3cm,微调精度达1μm.     

Tunable terahertz radiation from arbitrary profile dielectric grating coated with graphene excited by an electron beam

In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.     

Cherenkov terahertz radiation from Dirac semimetals surface plasmon polaritons excited by an electron beam

We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band.     

Polarization characteristics of stimulated emission of organic molecules when excited by intense XeCl laser radiation

We study the influence of the molecular structure, medium, and exciting-radiation parameters on the polarization, energy, and spectral characteristics of the emission of laser-active media based on the dicarboxylic derivative of p-terphenyl, rhodamine 101, and phenalemine 512. We found that the polarization of the stimulated emission of molecules when strongly excited under the conditions studied significantly depends on their structure, the pumping mode, the intensity and polarization of the exciting radiation, the shape and dimensions of the excited volume, and the phase state of the medium.     

Performance of a ten-liter electron avalanche-discharge XeCl laser device

This paper describes the laser performance of an X-ray preionized ten-liter volume, electron-avalanche discharge XeCl system, operated at dc charging voltages of up to 70 kV both with and without X-ray preionization. An output energy of more than 11J uniformly distributed over a (7×10) cm² spot size was achieved using a multichannel spark-gap as the main discharge switch. The discharge was also successfully operated in the switchless mode, yielding a 4.8 J output energy and a 0.9% efficiency. The time-resolved gain measurements provided information on the laser discharge evolution.ENEA GuestENEA Guest on leave from the Shanghai Institute of Optics and Fine Mechanics, the Chinese Academy of Sciences, Shanghai, China     

Numerical modeling of a XeCl laser excited by microwave discharge

12 , 169 (1987). Reasonably good agreements in the peak output power and laser efficiency have been achieved. Model calculations also predict that an efficiency as high as 2.7% can be obtained once the conditions of the above-mentioned experiments have been optimized. From the consideration that the skin depth effectively limits the absorption length of the microwave pumping and hence the excitable volume, it is concluded that high input power densities (>2 MW/cm³) and higher gas pressures (between 3 and 10 atm) are the preferable conditions to achieve higher efficiency. Preliminary calculations on CCl₄ containing XeCl gas mixtures show that improvement in laser efficiency by several folds may be achieved as a result of the higher intrinsic efficiency of excimer formation. Received: 23 September 1996 / Revised version: 25 March 1997     

Plasma instabilities excited by an azimuthal electron beam

The paper describes the effect of the finite temperature T of an azimuthal electron beam on plasma stability. Only instabilities for which the longitudinal macroscopic velocity of the beam is of no importance are discussed. It is shown that at the limit of applicability the weak and strong inhomogeneity approximations give the same results.     

Polarization effects of electron current settling when the cerenkov radiation is excited by a nonrelativistic electron beam in an open dielectric resonator

We study the effect of electron current settling of a strip nonrelativistic electron beam (EB) on the Cerenkov radiation (CR) in a metal-dielectric channel formed by the metal surface and the surface of a rectangular open dielectric resonator having isotropic properties and operated at millimeter wavelengths (3.6–5.8 mm). The choice of this channel was substantiated by theoretical studies of the CR energy density. We experimentally examined several effects, including the neutralization of the dielectric surface dipole charge by electrons, the accumulation of electron charge at the dielectric surface, and the influence of the electron charge on the EB and CR. Conclusions are drawn on the prospects of using short pulses of EB and special metal-dielectric diffraction gratings for the excitation of CR. Institute of Radioengineering and Electronics, Ukrainian National Academy of Sciences, Kharkov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 491–505, April, 1997.     

A study of the electron quenching of excimers in a KrF* laser excited by a coaxial electron beam

Measurements of the output energy, the optical pulse length and the build-up time of the laser pulse, obtained with a coaxially e-beam pumped KrF^* laser, were performed varying the total gas fill pressure, the F₂ content and the e-beam current from 1–5 bar, 0.1–0.8% and 13.3–26.6 kA, respectively. The maximum specific extraction energy amounts to 64 J/l. The large range of measurements, especially at low F₂ concentrations, reveals the necessity to extend the kinetics of the F₂ chain in the usual computer model. With the introduction of electron quenching of KrF^* and ArF^* by dissociative attachment the predictions are also for low F₂ concentration in agreement with experiments.     

Plasma radiation emitted by dense mixtures of rare gases excited by an electron beam and by a discharge

An experimental investigation was made of the radiation emitted from a plasma formed by rare gases (He, Ne, Ar, Kr, Xe) excited by a beam of electrons with different parameters and by discharge pulses (P= 0.1–0.5 atm, I=1 kA, U=10–15 kV, C=0.25 F). An investigation was made of the spectral composition and time characteristics of the radiation, and of their dependences on the excitation conditions. New molecular bands were observed in the near-ultraviolet and visible ranges. The uniquely large widths of these bands could be of interest in the amplification of light in a wide spectral range.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 56–73, January, 1992.     

Superlight source of radiation with a waveguide used for bunching an electron beam

A scheme of a generator of electromagnetic-wave radiation is proposed in which a radiating region moves along a radiator with a velocity greater than the velocity of light in vacuum. The superlight motion of the generating region leads to the situation in which the resulting radiation has the properties of Vavilov-Cherenkov radiation. The electron beam of a superlight source is formed while the particles travel across a waveguide along which an electromagnetic wave propagates. The construction of the generator makes it possible to vary the velocity of the radiating region, the radiation pattern, and the radiation beamwidth. Calculations are performed that allow one to evaluate the parameters of the generator and the characteristics of radiation.