Demonstration of a neonlike argon soft-x-ray laser with a picosecond-laser-irradiated gas puff target

We demonstrate a neonlike argon-ion x-ray laser, using a short-pulse laser-irradiated gas puff target. The gas puff target was formed by pulsed injection of gas from a high-pressure solenoid valve through a nozzle in the form of a narrow slit and irradiated with a combination of long, 600-ps and short, 6-ps high-power laser pulses with a total of 10 J of energy in a traveling-wave excitation scheme. Lasing was observed on the 3p (1)S(0)?3s (1)P(1) transition at 46.9 nm and the 3d (1)P(1)?3p (1)P(1) transition at 45.1 nm. A gain of 11 cm(-1) was measured on these transitions for targets up to 0.9 cm long.     

Extreme ultraviolet tomography of multi-jet gas puff target for high-order harmonic generation

A volume, tomographic reconstruction of a novel, multi-jet gas puff target, developed for possible applications in high-order harmonic generation (HHG), is presented. The target, produced by pulsed injection of argon gas through nozzle in a form of linearly oriented small orifices, has been characterized in the extreme ultraviolet at 13.5 nm wavelength. Target density estimations were performed, and 3-D representation of pulsed gaseous target has been obtained by combining 2-D shadowgram images, recorded at various rotation angles. More detailed information about higher-order jets, formed as a result of collisions of primary jets, was obtained. Tomographic studies of such type of targets dedicated for HHG have been obtained to our knowledge for the first time.     

Strong temperature effect on X-ray photo-etching of polytetrafluoroethylene using a 10 Hz laser-plasma radiation source based on a gas puff target

The first results of experiments on direct photo-etching of heated PTFE using a 10 Hz X-ray source based on a laser-irradiated gas puff target are presented. X-ray radiation in the wavelength range from 6 to 20 nm was produced as a result of irradiation of a double-stream gas puff target with Nd:YAG laser pulses of energy 0.8 J and time duration 3 ns. The resulting X-ray pulses with energy of about 100–200 mJ were used to irradiate samples of PTFE to create microstructures by direct photo-etching. Strong enhancement of the photo-etching process was observed for samples heated up to 300 °C. PACS 52.38.Ph; 81.65.Cf; 61.82.Pv     

Deposition of plasma-polymerized acetylene by an intense pulsed RFplasma source

An inductively coupled, intense, pulsed RF plasma source deposited plasma-polymerized acetylene at a rate of 127 Å per discharge. The potassium bromide substrate was located 18-cm downstream from the RF coil. A puff valve admitted parent acetylene gas just before the transient RF current was applied. Fourier transform infrared (FTIR) spectra showed that carbon-to-carbon double bonds were formed. Scanning-electron-microscope images showed that the film thickness after 79 discharges was 1 μm. A photodiode showed substantial light emission for about 30 μs during each discharge     

Spectral characterization of EUV radiation emitted from a laser-irradiated gas puff target

A laser-plasma EUV source is described, which is going to be utilized for characterization of EUV optical components and sensoric devices in the wavelength region from 11 to 13 nm. EUV radiation is generated by focusing a Nd:YAG laser into a double stream gas puff target. By the use of different target gases, broadband as well as narrow-band EUV radiation can be obtained. The emission characteristics of the radiation is monitored by the help of different diagnostic tools including a pinhole camera, an EUV spectrometer, and various EUV photodiodes, either directly or after reflection from multilayer mirrors. Theoretical calculations of collision-induced energy transfer are given in order to explain the observed high degree of electronic excitation in the utilized target gases.     

Submicron focusing of XUV radiation from a laser plasma source using a multilayer Laue lens

The focusing properties of a one-dimensional multilayer Laue lens (MLL) were investigated using monochromatic soft X-ray radiation from a table-top, laser-produced plasma source. The MLL was fabricated by a focused ion beam (FIB) structuring of pulsed laser deposited ZrO₂/Ti multilayers. This novel method offers the potential to overcome limitations encountered in electron lithographic processes. Utilizing this multilayer Laue lens, a line focus of XUV radiation from a laser-induced plasma in a nitrogen gas puff target could be generated. The evaluated focal length is close to the designed value of 220 μm for the measurement wavelength of 2.88 nm. Divergence angle and beam waist diameter are measured by a moving knife edge and a far-field experiment, determining all relevant second-order moments based beam parameters. The waist diameter has been found to be approximately 370 nm (FWHM).     

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采用迭代法对HL-2A装置1MW中性束系统中的中性化气体靶厚进行了理论计算,并给出了相应的中性化效率,发现仅靠离子源顺流气体形成的气体靶通常不能使中性化效率达到最佳值,因而有必要在中性化器内加入补充送气来提高气体靶厚。采用补充送气系统,在相同的放电参数下中性化效率提升约10%。     

Soft X-ray point source based on a gas pinch

The results of a study of a radiating Z-pinch with a profiled initial gas-density distribution over the z axis are presented. The gas distribution with the density maximum and transverse-size minimum at the discharge-gap center is formed by a pulsed gas valve with a specially designed nozzle. The parameters of X-ray radiation are measured for pinches formed in gaseous neon at currents of up to 200 kA. The experimentally selected gas density ensures the formation of a region with a typical size of less than 1 mm at the discharge-gap center. This region emits X-ray radiation in the keV photon-energy range in a time of less than 5 ns. Prospects for the development of an X-ray source based on this mechanism are discussed.     

透射式X光管研制

X光管是X射线源的关键部件,为了研制出便携式X射线标定源,研制了一种透射式X光管。该X光管是一个密封的电子束真空二极管,其阴极为竖直的梳齿状结构,电子更容易发射;靶窗为100μm厚的钛片;内部为真空腔,使用95陶瓷作为真空界面绝缘体,采用金属-陶瓷封接工艺,真空度达到5×10^-5 Pa。实验结果表明,所研制的X光管在距靶窗20 cm处剂量约为20 mR,此时X射线的脉冲宽度约为5 ns。     

中国脉冲功率科技进展简述

从脉冲功率科学技术的基本内涵出发,回顾我国脉冲功率发展历史,按照高功率脉冲加速器建设历程,我国脉冲功率技术发展史可大致分成三个阶段:自主创业、加速成长到创新超越;尝试以国际视野介绍我国在闪光照相、Z箍缩、高功率微波、电磁发射和工业应用等方面的发展成就;简要阐述脉冲功率技术未来发展趋势,建议大力发展先进辐射源技术,关注爆磁压缩技术,加强HPM、抗核加固和电磁发射等各类负载技术攻关,加大协同创新和应用推广。     

喷气Z箍缩X光辐射信号分析

 在清华大学喷气Z箍缩平台上进行了对Ne气的箍缩软X射线诊断工作。该喷气装置由4个充电至23 kV的电容器并联组成，总储能4.5 kJ，放电电流峰值210 kA，上升沿2.5 ms。实验中通过观测放电电流微分信号来观测箍缩聚焦点的位置（波形的下凹尖峰点），此尖峰也是X光辐射的时间分辨点。利用响应时间为亚ns量级的光敏半导体探测器(PIN)探头获得了Ne气箍缩时等离子体发出的软X射线信号，X光辐射出现在放电电流微分信号突变点附近。一般来说，多次箍缩会导致多次的X光辐射输出，实验中的X光脉冲实际为多个等离子热点辐射叠加的结果，单次箍缩所产生的X光辐射比多次箍缩所产生的X光辐射要强。对每次箍缩来说，单个X光脉冲信号比多个X光脉冲信号的幅值要大。     

Emission induced by collision of two plumes during pulsed laser ablation

We observed plume expansion dynamics during pulsed laser ablation when two plumes collided head-on. Si and Ge targets were placed parallel each other, and they were irradiated simultaneously by two pulsed lasers. A new emission appeared near the center of the targets from 250 ns after the irradiation. However, the predominant ejected species is neutral SiI or GeI at this time region when an individual single target is irradiated, and the new emission emerged by collision is a mixture of ionized SiII and GeII. This indicates that the kinetic energy of the collision excites the species to an ionized state. The intensity of this new emission decreased by increasing the background gas pressure. This suggests that collision between two plumes induces a higher-temperature plasma. Since the new emission is composed of ionized Si and Ge species and remains a relatively long period after the collision, this technique will provide a new reactive field to prepare a new kind of alloy nanomaterials.     

Water-window microscopy using a compact, laser-plasma SXR source based on a double-stream gas-puff target

We report on a compact, desktop size, laboratory type microscopy setup, based on a short wavelength gas puff target soft X-ray source, which emits incoherent radiation in “water-window” spectral range. The microscope employs a Wolter type I reflective objective and allows capturing magnified images of objects with ~1-μm spatial resolution and exposure time as low as 5 s. A detailed characterization and optimization of both the source and the microscope setups are presented and discussed.     

Arc erosion reduction on electrical contacts using transversecurrent injection

Electrical contact lifetime is often directly determined by arc erosion. A method for reducing are erosion was developed consisting of injecting from an external current source an additional electrical current flowing parallel to the contact surface. This method was examined in three are environments using the additional transverse electrical current with a density less than 1 A/mm²: 1) automobile ignition contacts; 2) pulsed air arc; and 3) low pressure (P=100 mTorr) arc in nitrogen, SEM and X-ray examination showed that application of a transverse current in a contact during arcing changed the phase composition and microstructure of the contact surface. Under optimal conditions, the microstructure which is formed is significantly more erosion resistant than without the transverse current injection     

Analysis of the interface between a pulsed laser deposited calcium phosphate coating and a titanium alloy substrate

Calcium phosphate coatings deposited on titanium alloy are intended to add a bioactive surface to medical implants. This work presents the characterisation of the interface between Ti-6Al-4V and a crystalline calcium phosphate coating obtained by pulsed laser deposition, with a KrF excimer laser, at 575 °C and under a 45 Pa water-vapour atmosphere. The coating–substrate system was studied by secondary-ion mass spectrometry, scanning electron microscopy, X-ray diffractometry, Raman spectroscopy and X-ray photoelectron spectroscopy. The results show that the deposition process promotes the interdiffusion of substrate elements into the coating and coating elements into the substrate oxide layer. Thus, a graded layer of mixed calcium phosphate and amorphous titanium oxide is formed. For the substrate, a hydroxyapatite coating acts more as a barrier for oxygen incoming from a gas than as an oxygen source during deposition. Moreover, oxygen diffusion into the substrate occurs. Thus, the content of oxygen of this oxide layer diminishes with depth. When the oxygen concentration is low enough it is incorporated in solid solution in the titanium alloy . PACS 81.15.Fg; 68.55.-a; 87.68.+z     

放电参数对爆燃模式下同轴枪强流脉冲放电等离子体的影响

同轴枪强流脉冲放电常见有爆燃模式和预填充模式两种放电模式,爆燃模式放电可以得到杂质少、准直性高、输运速度更快的等离子体射流.本实验主要对不同电压及进气量下同轴枪强流脉冲爆燃模式放电的等离子体特性进行了研究.结果表明,在相同放电电压下,进气量少时会有多团等离子体从枪口喷出.随着进气量的增加,同轴枪放电产生的等离子体密度增加,输运速度减小,最终等离子体只有一团从枪口喷出;而在相同进气量下,随着电压的增加,等离子体密度增加,输运速度增大,开始出现有多团等离子体从枪口喷出的现象.产生该现象的原因主要是在放电过程中,当气体持续进入枪底部时,同轴枪底部会产生新的电流通道向前运动,使得在同轴枪出口处观察到了多团等离子体喷出的现象;随着放电电压的增加,在放电过程中回路电流也增加.当电流增加到一定程度时,同轴枪底部就会产生新的电流通道,从而有多个等离子体团从枪口喷出.通过改变充电电容以及对磁探针信号的分析,进一步分析并验证了同轴枪底端多次放电的现象.     

多相脉冲放电体系中羟基自由基的光谱诊断

采用多针-板电极形式的气液混合脉冲放电系统,在其中加入玻璃珠负载的TiO₂膜光催化剂形成了一个气-液-固多相脉冲放电体系,研究中利用脉冲放电过程中产生的紫外光效应诱导其中的TiO₂的光催化作用,通过对放电体系中羟基自由基(·OH)的光谱诊断考察TiO₂光催化作用与脉冲流光放电的协同作用效果。结果表明,本脉冲放电体系中产生的·OH在306 nm(A2Σ+→X2Π跃迁)、309 nm(A2Σ+(ν′=0)→X2Π(ν″=0)跃迁)和313 nm(A2Σ+(ν′=1)→X2Π(ν″=1)跃迁)处均产生发射光谱,其中313 nm处的·OH的光谱强度最强;脉冲放电协同TiO₂光催化作用系统中·OH的发射光谱强度较单独的脉冲放电体系强,同时,条件实验(不同鼓气种类和水溶液初始pH值)的研究结果表明用氩气作为鼓气源时,多相反应体系中313 nm处·OH的发射光谱强度比以空气和氧气作为鼓气源时的强度高,酸性溶液中313 nm处·OH的发射光谱强度比中性和碱性溶液中高。     

Femtosecond X-ray line emission from multilayer targets irradiated by short laser pulses

The invention of high-power, ultra-short-pulse lasers has opened the way to investigations aimed at the creation of a new type of bright X-ray source for various uses including material science applications and time-resolved X-ray diffraction for biology. The efficiency with which laser energy incident on a solid target is converted into an X-ray emission depends on many factors, including the temporal profile of the laser pulse. Here we report the results of our theoretical and experimental investigations of the line X-ray emission from layered solid targets irradiated by ultra-short laser pulses. The laser prepulse parameters and target thickness are optimized to convert the maximum laser energy into an emission in the selected X-ray line. Multilayer foils are proposed to increase the energy of the K-line emission from laser plasma while simultaneously keeping the X-ray pulse duration at a hundred femtoseconds. The emission is studied both experimentally and theoretically by means of an analytical model and numerical simulations. PACS 52.38.Ph; 52.38.Dx; 52.50.Jm     

Formation of tight plasma pinches and generation of high-power soft x-ray radiation pulses in fast Z-pinch implosions

Argon K-shell plasma radiation source experiments were carried out on the GIT-12 generator [Bugaev, S.P. et al., 1997, Russian Phys. Journal, 40, 38] for a long (300 ns) implosion regime. The performance of a shell-on-solid-fill double gas puff was characterized in the experiments with and without an external axial magnetic field. The maximum Ar K-shell radiation yield registered in the experiments without an axial magnetic field was at the level of 1100 J/cm. This yield is consistent with the theoretically predicted yield for a short (100 ns) implosion regime. The experiments showed that the initial magnetic field which provides stabilization of the shell-on-solid-fill double gas puff was lower than that required for stabilization of a single annular gas puff. Satisfactory stabilization of the double gas puff was observed at an initial axial magnetic field of 1.4 kG. The maximum Ar K-shell radiation yield registered in the experiments with the axial magnetic field did not exceed 400 J/cm. A sharp reduction of the K-shell yield cannot be explained only by taking into account the energy losses associated with the compression of the axial magnetic field. Original Text ? Astro, Ltd., 2006.     

测量喷气Z箍缩负载的气流马赫数

 利用双压力传感器的方法测量了喷气Z箍缩负载的气流马赫数。测量得到的气流马赫数最高可达到4.25，它和定常计算的结果4.8很接近，这表明可以用定常计算来估算喷气Z箍缩中超声速喷嘴产生的气流马赫数。