毛细管放电Z箍缩等离子体X射线激光

毛细管放电Z箍缩等离子体软X射线激光器近几年发展非常迅速，已经获得了在46．9nm的波长上近毫焦量级的激光输出，重复频率达到了4Hz．利用这种软X射线激光在等离子诊断、物质烧熔等方面已开展了初步的应用实验研究．文章介绍了毛细管放电泵浦的两种物理机制，阐述了类氖氩离子2p^53p^1S0-2p^53s^1P1能级间粒子数反转的形成及毛细管放电等离子体柱的演变过程．深入理解这些物理过程，对发展毛细管放电软X射线激光将起到积极作用。     

Capillary discharge tabletop soft X-ray lasers reach new wavelengths and applications

For many years, researchers have envisioned the development of compact high repetition rate tabletop soft X-ray lasers that could be routinely used in application in numerous disciplines. With demonstrated average powers of several mW and mJ-level pulse energy at 46.9 nm, capillary discharge-pumped lasers are the first compact lasers to reach this goal. In this paper we summarize the development status of high repetition rate tabletop soft X-ray lasers based on capillary discharge excitation, and give examples of their successful use in several applications. Results of the use of a capillary discharge pumped 46.9 nm laser in dense plasma interferometry, soft X-ray reflectometry for the determination of optical constants, and laser ablation are described. The observation of lasing at 53 nm line in Ne-like Cl with output pulse energy up to 10 μJ is also reported.     

脉冲功率技术在短波长气体激光器中的应用

 介绍了脉冲功率技术在离子准分子、准分子和软X射线激光研究中的应用情况。给出了三种激光产生对泵浦源电学参数的要求,并给出实现这些电学参数的实验装置以及实验装置的性能指标。在软X射线激光研究方面,利用10级Marx发生器和Blumlein传输线,建立了最高电流峰值40 kA,前沿为26.6 ns的毛细管放电装置,并实现了46.9 nm激光输出。建立了输出电压600 kV、输出电流20 kA的电子束装置,并作为泵浦源实现了离子准分子光腔效应。为了泵浦S2准分子,采用横向放电方式和低电感放电回路,实现了电压脉冲宽度为29.2 ns的窄脉冲放电。     

Electromagnetic radiation of a nanosecond discharge in an open gas-filled diode

The properties of the discharge in and radiation from an open gas-filled diode to which high-voltage nanosecond pulses are applied from the RADAN-220 generator are studied. Electromagnetic radiation in the X-ray, UV, visible, and near-IR ranges of the spectrum, as well as high-power subnanosecond (0.5-to 0.7-ns-long) pulses of ultra-wide-band (UWB) electromagnetic radiation, are recorded when a diffuse discharge is initiated in atmospheric pressure air. For the coaxial cathode and anode, the open gas diode emits radially polarized UWB pulses, whereas for the cathode in the form of a segment, the UWB radiation is linearly polarized. The effective potential for both designs of the diode is ER = 6 kV. It is shown that the plasma in the discharge gap serves as a source of soft X rays and the metallic anode generates hard X rays.     

Some design limitations for large-aperture high-energy per pulse excimer lasers

Summary Some limitation problems for gas discharge excimer lasers, when scaled to a high pulsed energy output with high repetition rate are discussed. As an example, we present some experimental results obtained with an X-ray preionized (10×10×100) cm³ active volume, low-repetition-rate-operated gas discharge XeCl laser system. ENEA student. ENEA guest.     

Feasibility of a laboratory X-ray laser pumped by ultrashort UV laser pulses

In order to allow widespread application of soft X-ray lasers there is a strong effort worldwide to use as small as possible pump lasers for plasma production. Short pulse lasers ( 1 ps), particularly in the UV, have attracted much interest, since extremely high intensities (up to 10¹⁸ W/cm²) can be achieved with a relatively high repetition rate. In this article we discuss their merit for soft X-ray laser pumping and possible solutions to the specific problems, for instance pulse front distortion, nonlinear absorption in window materials, plasma formation by short laser pulses and the relatively low total pump energy.     

Enhancement of soft X-ray emission from a pinch plasma using a rotating plasma for pre-ionization

An experimental study on the enhancement of soft X-ray emission from a pinch plasma has been carried out by using a rotating plasma for pre-ionization. The rotating plasma is produced by a pulsed J×B cross-field discharge between coaxial electrodes, and subjected to a pinch discharge. Under an optimized discharge condition, it has been observed that UV emission of 251.6 nm (Ar III) soft X-ray intensity increases with increasing applied axial magnetic field B. At 400 G, the X-ray intensity is enhanced by a factor of 3 compared to that without the rotating plasma. It is considered that this result is due to the improved characteristics of the pre-ionization rotating plasma, which influences the uniformity and stability of subsequent pinch plasma.     

Excimer lasers and laser systems

The results of the experimental study of UV lasers and laser systems pumped by different methods are presented. Two lasers were pumped by electron beams from Marx generators. Three lasers were pumped by transverse discharge with UV preionization. An XeCl laser pumped by electric discharge using a generator with inductive energy storage and semiconducting opening switch is investigated. The highest laser radiation energies of 2000, 90, and 0.7 J have been obtained at 5=308, 249, and 222 nm, respectively. The amplification of the laser beam from the master oscillator under conditions of strong amplified spontaneous emission is considered. In particular, formation of the output from an amplifier in the wings of the XeCl laser band and in the case of a large-aperture XeCl amplifier are investigated. The output beam divergence in these experiments was measured to be ~10^-4 rad.     

Pulsed lasers pumped with a self-sustained discharge

The results of investigations of UV, visible, and infrared lasers pumped by a self-sustained discharge and operating by transitions of molecules, atoms, and ions are presented and the laser constructions are described. For excitation of the working mixtures, generators with capacitive and inductive energy stores and various preionization systems were used. Optimum conditions for pumping various lasers have been found and simple and reliable prototypes of exciplex, nitrogen, HF, CO₂, and other electric-discharge lasers (Foton, LIDA, DILAN, AIL, and ELAN) for scientific research have been created. Radiation energies from some fractions of a millijoule to 3 J have been obtained for a number of transitions at wavelengths ranging between 157 and 10,600 nm with a high efficiency. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 45–53, April, 2000.     

Energy distribution of runaway and fast electrons upon nanosecond volume discharge in atmospheric-pressure air

Nanosecond space discharge in a gas-filled diode is promising for pumping of lasers and high-power lamps. The space charge formed in the absence of an additional preionization source has a few advantages. The energy distributions of the beam electrons and the X-ray spectrum are determined. It is demonstrated that several high-energy electron bunches are formed in such a discharge. The main contribution to the beam current measured behind the foil is related to the runaway electrons, which have energies of tens or hundreds of kiloelectronvolts (supershort avalanche electron beam (SAEB)). Fast electrons with energies of several or tens of kiloelectronvolts are responsible for the generation of the soft X rays in the discharge gap. Anomalous electrons whose energy is higher than the voltage across the gap provide for a minor (less than 5%) contribution to the beam current. The generation time of these electrons is equal to the SAEB generation time accurate to 0.1 ns. It is demonstrated that the anomalous electrons can be generated owing to the acceleration in the presence of the field in front of the moving background-electron multiplication wave. The spectra of the X-ray radiation generated by the fast electrons in the volume are calculated.     

Studies of advanced soft X-ray laser and coherent higher harmonic generation using intense subpicosecond laser produced high density plasma

Current activities on our research of soft X-ray lasers and higher harmonic generations using intense, subpicosecond lasers are reviewed. Especially for soft X-ray lasers we experimentally demonstrate that by longitudinally pumping 2-mm-long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft-X-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submilliradian order, and only requires pump laser energy of 150 mJ. Simulations show that the pedestal in the main pump pulse can generate electron density and gain profiles with large spatial gradients, which result in the selective amplification of low-order transverse modes. The present result is the demonstration of an efficient and alternative method of improving the spatial coherence of X-ray lasers with amplified spontaneous emission medium, with possibilities of becoming an excellent tool to explore various application experiments. In higher harmonic generation, topics related to observation of blue shift due to collisionless absorption process is described.     

Parametric study of plasma active medium and gain saturation region in a Ne-like soft X-ray laser

Plasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X-ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X-ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double-pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne-like germanium soft X-ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X-ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X-ray laser intensity with 294 cm⁻¹ gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium.     

Visible iodine and bromine laser,and coaxial discharge excited strong UV iodine laser

Nine new Br and I ion laser lines in the visible and the UV regions were observed by ordinary longitudinal pulsed discharge or coaxial pulsed discharge. This is the first time that the UV I ion laser was obtained with an output much stronger than that of ordinary pulsed ion lasers. The characteristics of the laser output were investigated in the case of coaxial discharge.     

激光软X—射线近贴显微技术初步研究

描述了用高功率脉冲激光打靶产生的等离子体作为软X-射线源而进行的近贴显微研究,并得到了分辨率好于1μm的结果.     

Laser-excited fluorescence of perylene by using self-induced second-harmonic and sum-frequency radiation emanating from high-power AlGaAs double hetero-type diodes

High-power (12 W) pulse-operated AlGaAs double-heterostructure lasers with a large thickness of the active layer (1.5 µm) are able to produce internal second-harmonic and sum-frequency generation with a peak power of 10 mW. The corresponding portion of the electroluminescence spectra has a maximum at 405 nm. Clearly resolved mode structures of the fundamental and harmonic radiation are analysed in detail. Particular transverse modes exhibit different conversion efficiencies. Violet resonances without modal precursors in the infrared spectrum make a marked contribution to the light intensity. The harmonic signal serves as an excitation source in photoluminescence studies. A technique of single-photon counting is applied in order to perform spectral measurements under weak-intensity levels. Bright fluorescence spectra of saturated solution of perylene ino-xylene are presented. The spectrum obtained when the solution is illuminated with a gas discharge lamp shows no differences with respect to the positions of the intensity peaks. This allows us to suggest that AlGaAs high-power lasers can be used as convenient excitation sources in photophysics, in particular in time-resolved experiments.     

A statistical study of the relation between soft X-ray excess and accretion disk

To study the origin of the soft X-ray excess, we compile a sample of 94 unobscured, radio-quiet QSOs and Seyfert galaxies with available data from GALEX and ROSAT. We find that 50 sources show strong soft X-ray excess and the other 44 show weak/no soft X-ray excess. Systematic analyses of the data indicate that the difference in soft X-rays is mainly but not only resulting from different accretion rates (in units of Eddington rate). The statistical study of the sources with soft X-ray excess shows that the strength of soft X-ray excess weakly and positively correlates with the Eddington ratio and increases with the increase of the strength of UV radiations relative to the X-rays. Provided that the UV emissions are from the thin disk, the correlations imply that the origin of soft X-ray excess is associated with the thin disk, either by means of Comptonization of the disk photons or in some other ways.

     

Thermal instability of glow discharge in the gas loop of CO2 laser with extended disk fans-heat exchangers

CO₂ lasers with transverse discharge and convective gas cooling find ever-increasing application. On strategy in making such lasers more efficient radiators is increasing the rate of the gas flow through the discharge zone with the help of diametral disk fans-heat exchangers. The application of such fans-heat exchangers, however, entails serious difficulties related to the glow discharge-gas flow interaction. In the present study, we investigate the stability problem for volume discharge in the gas loop of a CO₂ laser with diametral dis fans-heat exchangers.     

Study of the limiting energy characteristics of a combined discharge in a gas flow

A combined method of excitation of a gaseous medium is used in an investigation of the energy characteristics of a non-self-sustaining discharge as functions of the capacitance of the capacitor bank, the number of pulses per burst, and the burst repetition rate for different time intervals between the pulses in a burst and different flow velocities of the gas. It is shown for infrared lasers that under optimal pumping conditions the average discharge power can reach 8.5 W/cm³ for a pulse power of 25 W/cm³. Zh. Tekh. Fiz. 68, 33–38 (May 1998)     

Electrode surface erosion in a high-frequency discharge plasma

The surface erosion of electrodes made of different materials in the plasma of a high-frequency discharge, which is used for pumping ion lasers at a frequency of 10 MHz, is investigated. It is found that the erosion is due to blistering. The effect of the electrode temperature and material, as well as of the gas type, on the erosion evolution under typical operating conditions of a gas discharge tube is studied. The concentration of blistering products (dust particles) in the discharge is estimated in the framework of geometrical optics. Ways to prevent blistering in the discharge under such conditions are suggested.     

Electromagnetic radiation sources based on a low-inductive extended z-discharge

Model sources of electromagnetic radiation based on a low-inductive extended z-discharge are studied experimentally and numerically. The discharge is initiated by a high-voltage pulse generator through a long transmission line. It is shown that using a sliding discharge traveling wave, one can provide electrical breakdown of long discharge gaps in a wide range of initial gas pressure and produce a plasma pinch at moderate voltages of the generator. A new nonpinch mechanism of radiation generation is discovered in the soft X-ray range of the spectra. This mechanism offers a higher efficiency of conversion of electrical energy to the energy of an inverted medium.