软X射线激光偏折法测量激光等离子体电子密度分布

利用脉宽约为50ps的类镍银139nm软X射线激光作为探针,探测由脉宽80ps的驱动激光打C8H8靶产生的等离子体在1ns后的电子密度分布信息,获得了清晰的莫尔条纹图像.对结果的处理,给出了峰值电子密度为11×1021cm-3,并对在靶面附近莫尔条纹的消失现象作了初步解释 关键词： 软X射线激光探针 莫尔条纹 等离子体电子密度     

Design of capillary Z-pinch plasma for a soft X-ray laser

An analysis for designing capillary Z-pinch plasma as an alternative active medium of soft X-ray laser is presented. The validity of calculation results are verified by experiment. Namely, the specification of driving current as well as the predicted pinch time is in good agreement with the experimental results. This study also reveals the possibility of reducing the main charging voltage without degrading the performance of the X-ray laser.     

A low debris laser plasma soft X-ray source

Low debris laser plasma soft X-ray source is of great importance to micro-lithography and microscopy. In this paper, a 1.06 μm YAG laser with 2 J energy, 10 ns duration is employed to irradiate a CO₂ cryogenic target. Soft X-ray spectra from the CO₂ cryogenic target are obtained. Experimental results of debris measurement from both CO₂ cryogenic and Cu targets demonstrate that the light source based on the CO₂ cryogenic target shows great improvement over conventional metal targets in debris reduction.     

软X射线激光探针诊断高$lt;i$gt;Z$lt;/i$gt;材料等离子体

激光辐照靶产生的等离子体电子密度的诊断对于惯性约束聚变、高能量密度物理等相关领域的研究具有重要意义,特别是高Z材料等离子体临界面附近的电子密度分布信息的测量. 利用软X射线激光作为探针是诊断等离子体电子密度分布的一种重要方法,但在诊断激光辐照高Z材料产生的等离子体研究中,遇到了高Z材料等离子体自发辐射过大的问题,难以开展. 为此,针对软X射线激光的特点,发展了多种具体的实验技术. 通过综合利用这些技术,大大的抑制了待测等离子体自发辐射对信号的影响,使得软X射线激光探针诊断高Z材料等离子体成为可能. 作为典型例子,实验诊断了激光辐照金平面靶的等离子体,获得了清晰的实验图像,表明相关的技术是有效和可行的. 关键词： 等离子体诊断 激光探针技术 软X射线激光 Z材料等离子体')" href="#">高Z材料等离子体     

Investigations on laser plasma soft X-ray sources generated with low energy laser systems

Spectra of laser-induced plasmas at low laser energies and intensities (around 100 mJ and 10¹⁰ W cm^–2 respectively) have been recorded in the spectral range of 20 to 100 nm for different target materials, laser intensities at the target and laser wavelengths. For heavy target materials, a broadband spectrum with a spectral maximum typically around 30 nm is obtained. This broadband radiation source is well suited for photoionization processes and the generation of short wavelength inner-shell photoionization lasers. For the cadmium-photoionization laser, the influence of different soft X-ray spectra on the laser energy has been investigated. The potential of laser plasma soft X-ray sources for scientific and technical applications is briefly reviewed.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Space-resolved soft X-ray emission from laser produced lithium plasma

Space-resolved emission spectroscopy was used to study the evolution of 13.5 nm line intensity and electron temperature of the plasma generated by laser ablation of lithium target. Two emitting regions were observed, their intensities depending on laser fluency. Plasma image is discussed in the frame of a Gaussian model of particle expansion.     

Key methods for intensifying soft X-ray emission from a laser plasma for lithography

A two-pulse two-wave (Nd and CO₂ lasers) scheme is proposed for irradiating a laser target, which ensures the highest factor of laser radiation conversion to the X-ray range (13.5 nm ± 1%). Analytic estimates are obtained for parameters of pulses and of the target made of Xe or Li. Numerical optimization is performed for X-ray emission from a spherical Xe target exposed to a CO₂ laser pulse. The maximal factor of conversion of laser radiation to X rays is ～1%. Angular and spectral characteristics of X-ray radiation are obtained. The flux of fast Xe ions ejected from the target and damaging the Mo/Si coating of X-ray mirrors is estimated.     

半圆柱壳槽靶的激光等离子体软X射线光谱发射特点的研究

通常对一种半圆柱壳槽靶与平面靶激光等离子体软X射线光谱空间分布特点和流体动力学行为的比较,证实这种槽形靶可以有效地提高槽区内等离子体温度,从而增强该区域内的软X＇射线光谱发射.     

Characterization of compact bright soft X-ray source based on picosecond laser plasma

Radiation emission of silicon and aluminum plasmas produced by 40-ps laser pulses with peak intensity above 10¹⁴ W/cm² was studied. High-resolution soft X-rayspectra of H-like and He-like ions were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the intercombination lines of He-like ions with the results of model calculations. Such comparisons gave average values of the electron number density N_e=(1-1.9)×10²¹ cm^-3 and the electron temperature T_e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. The plasma size is about 100 μm. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π during the total decay period. PACS 41.50.+h; 52.25.Os; 52.50.Jm     

Ablation process of silica glass induced by laser plasma soft X-ray irradiation

Silica glass can be machined by irradiation with laser plasma soft X-rays on nano- and micrometer scale. We have investigated the ablation process of silica glass induced by laser plasma soft X-ray irradiation. We observed ionic and neutral species emitted from silica surfaces after irradiation. Dominant ions and neutrals are O⁺ and Si⁺ ions and Si, O, SiO and Si₂ neutrals, respectively. The ions have kinetic energies of 13 and 25 eV, which are much higher than those of particles emitted by evaporation. The energy of laser plasma soft X-rays absorbed to silica glass at a fluence of 1.4 J/cm² is estimated to be 380 kJ/cm³, which is higher than the binding energy of SiO₂ of 76 kJ/cm³. These results suggest that the most of the bonds in silica glass are broken by absorption of laser plasma soft X-rays, that several percent of the atoms are ionized, and that neutral atoms are emitted together with repulsive ions. The process possibly enables us to fabricate nano structures.     

Study of the X-ray emission from Ta plasma obtained by ns laser ablation

In this work, the continuum spectrum of X-rays originated from the interaction of a moderate intensity ns Nd:YAG laser (1064 nm, 9 ns, 30 Hz, 900 mJ, 10¹¹ W/cm²) with Ta target producing plasma is investigated. Plasma expands unisotropically with a velocity, depending on the pressure of the residual gas in the vacuum chamber. The X-ray intensity is a function of the laser energy and of the gas pressure inside the chamber. The X-ray energy is measured with an X-ray filter positioned in front of the Si(Li) solid-state detector. A temperature of about ～1–2 keV of the hot electrons, responsible for the continuum spectrum emission from the plasma, is calculated from the fit of the X-ray spectrum, applying a Maxwellian distribution.     

Absorption of a laser light pulse in a dense plasma

An experimental study of the absorption of a laser light pulse in a transient, high-density, high-temperature plasma is presented. The plasma is generated around a metallic anode tip by a fast capacitive discharge occurring in vacuum. The amount of transmitted light is measured for plasmas made of different metallic ions in the regions of the discharge of high electronic density. Variation of the transmission during the laser pulse is also recorded. Plasma electrons are considered responsible for the very high absorption observed.     

Nonlinear interaction of a circularly polarized electromagnetic wave with a dense laser plasma

The interaction of an intense circularly polarized laser pulse with a layer of plasma of supercritical density is studied. The nonlinear skin effect for the electromagnetic field and the coefficient of collisionless absorption of the laser pulse were calculated analytically. It is shown that, in the process of interaction with the plasma, the laser pulse generates solitons propagating through the plasma layer and transferring the radiation through the opaque medium. The coefficient of transparency of the plasma layer for the soliton-like penetration of the laser radiation was calculated. The plasma parameters at which the collisionless absorption is small as compared to the transformation of the laser energy into solitons were found.     

Scope of plasma focus with argon as a soft X-ray source

The X-radiation emission from a low energy plasma focus with argon as a filling gas is investigated. Specifically, the attention is paid to determine the system efficiency for argon K-lines and Cu-K/sub /spl alpha// line emission at different filling pressures, and identify the radiation emission region. The highest argon line emission found at 1.5 mbar is about 30 mJ and the corresponding efficiency is 0.0015%. The same pressure is suitable for high Cu-K/sub /spl alpha// emission, which is about 70 mJ in 4/spl pi/ geometry and the system efficiency is 0.003%. The bulk of X-radiation is emitted from the region close to the anode tip, whereas some radiation emission takes place from the formed hot spots along the focus axis. These radiations are found suitable for backlighting in Al (1-1.56 keV) and Ti (2.9-4.96 keV) energy transmission bands.     

Homogeneous focusing with a transient soft X-ray laser for irradiation experiments

We report the work done on a transient soft X-ray laser (SXRL) beam to deliver a proper extreme UV irradiation source for applications. The same optical tool was first demonstrated on a quasi stationnary state (QSS) soft X-Ray laser at the PALS Institute in Prague. The problem set by the transient soft X-Ray laser developed by the LIXAM at the LULI installation in Palaiseau is more crucial, first because the beam spatial profile is more irregular secondly because high repetition rate soft X-ray laser facilities in the future are based on this SXRL type. The spots obtained show a 20 micron average diameter and a rather homogeneous and smooth profile that make them a realistic irradiation source to interact with targets requiring relatively high fluence (near 1 J/cm²) or intensity (near 10¹¹ W/cm²) in the extreme UV domain.     

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.     

Interaction of a high-intensity ultrashort laser pulse with extended nanofilaments of dense plasma

Generation and propagation of fast electrons in laser targets consisting of thin nanofilaments are studied numerically and analytically. Such targets completely absorb laser radiation and exhibit a large coefficient of laser-energy conversion to kinetic energy of a flow of fast electrons. Analytical estimates show that the optimal thickness of the filament is on the order of the skin depth of the laser plasma, while an optimal distance between filaments is on the order of the Debye radius of hot electrons. A bunch of relativistic electrons can propagate as far as several hundred micrometers in such targets, while the fastest electrons can propagate several millimeters. Upon bending of filaments, the flow of electrons propagates along the filaments and can be focused by bringing the filaments together. Laser targets of the discussed composition are used as sources of dense bunches of relativistic electrons and subsequent generation of high-intensity X-ray radiation with their help.     

X射线激光在稠密等离子体诊断中的应用

X射线波段的相干辐射——X射线激光，由于其短波长、高强度、强相干等独特的优点，已经成为诊断稠密等离子体状态的一种工具．文章结合相应的应用演示实验对此进行了简要的描述，介绍了诊断的原理、X射线激光的获得，以及偏折法和干涉法诊断的实验及其结果．     

X射线激光在稠密等离子体诊断中的应用

X射线波段的相干辐射——X射线激光,由于其短波长、高强度、强相干等独特的优点,已经成为诊断稠密等离子体状态的一种工具.文章结合相应的应用演示实验对此进行了简要的描述,介绍了诊断的原理、X射线激光的获得,以及偏折法和干涉法诊断的实验及其结果.     

Hydrodynamics of a dense plasma created during laser annealing pulses

We show that an electron-hole plasma with density well above the droplet one (≈ 10¹⁸ cm^?3 in Si) expands very fast. Adding Auger recombination and phonon collisions, the maximum density for typical laser annealing pulses is found to be at most a few times 10²⁰ cm^?3. As a plasma density of a few times 10²¹ cm^?3 is necessary to modify the stability of the solid, we conclude that the laser pulse has essentially a thermal effect.