Stable and fully controlled long-time operation of a soft X-ray laser for user application experiments

Irradiation of user-supplied samples with pulsed 18.9 nm radiation originating from a molybdenum soft x-ray laser pumped in a double-pulse, single-beam (DGRIP) configuration is described. Stable operation at 10 Hz during up to 50,000 pulses is demonstrated with an average on-sample pulse energy of 200 nJ. The ability of the irradiation device to precisely deliver high photon doses with good spatial uniformity is confirmed. This constitutes to our knowledge the first demonstration of a laser-pumped soft x-ray laser as a stable and fully characterized irradiation source running automatically over exposure times of several hours.     

Longitudinal coherence and spectral profile of a nickel-like silver transient soft X-ray laser

The spectral width of a Ni-like silver transient soft X-ray laser (4d-4p λ= 13.9 nm) was experimentally inferred from the measurement of its temporal coherence, performed with a novel wavefront division interferometer. The measured coherence time of 3 ps corresponds to a spectral linewidth of 0.7 m? which is narrow. We compare this experimental result to numerical simulations of the amplified line profile, performed along two different approaches. Both calculations predict a spectral linewidth that is about 3 times larger than the experimental value. We discuss several effects that might explain this discrepancy. We show that, due to the short duration of the X-ray laser pulse, the assumption of a stationary electromagnetic field used in both the experimental analysis and in the calculations need to be reconsidered.     

Transverse scattering of radiation upon focusing of pump laser beam to line in experiments on X-ray laser

The force matrix of the SO₂ molecule is calculated without using a priori assumptions on the nature of the force field. The calculations are performed using a comparatively new 3N-matrix method based on the experimental frequencies of characteristic normal vibrations of ³²S¹⁶O₂, ³²S¹⁸O₂, and ³⁴S¹⁶O₂ molecules. It is shown that the direction of the chemical bond between chemically bound S and O atoms does not coincide with the direction of the straight line that connects the nuclei of these atoms. The angle between these directions (deviation angle) is determined. In the approximation of harmonic vibrations, the deviation angle is Δ = 1.092°. The effect of the anharmonicity of vibrations on the deviation angle is evaluated.     

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.     

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.     

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     

利用皮秒脉冲激光驱动瞬态X射线激光

报道了利用皮秒激光驱动产生瞬态类镍银X射线激光的实验结果.采用一路脉冲宽度为数百皮秒的激光作为预脉冲，配合另一路皮秒激光作为主脉冲联合驱动平面靶，获得了一定强度的类镍银X射线激光输出，输出能量约为5—10nJ. 关键词： 瞬态X射线激光 长短脉冲联合驱动 皮秒脉冲激光     

Shadowgrams of a dense micro-capillary plasma obtained with atable-top soft X-ray laser

A sequence of high resolution shadowgrams that map the evolution of the plasma of a 380 μm diameter microcapillary discharge was obtained using a very compact 46.9 nm laser. These images are the first plasma diagnostics data obtained using a table-top soft X-ray laser     

ICF实验软X光能谱的基函数解谱法

惯性约束聚变实验中,14通道软X光能谱仪是测量软X射线能谱、等效积分温度和辐射能流时间过程的重要诊断设备。基函数法是还原能谱分布的一种常用方法。通过对双峰谱形的还原,对不同类型基函数的选择、基函数参数的设置和求解方法等影响解谱的因素进行了比较分析。根据大量算例的结果,使用优化后的基函数和求解方法对实际测量辐射谱进行了计算,并与透射光栅谱仪的测量结果进行了比较。结果显示,根据谱仪通道响应选择三次样条的节点,能够较好还原软X射线的能谱。     

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.     

用于X射线激光实验研究的列阵柱面透镜线聚焦系统

用平行排列的柱面透镜列阵与非球面会聚透镜组成一个新颖的激光线聚焦系统,它能获得光强分布非常均匀的、能应用于X射线激光实验研究的高功率激光焦线。实验证明该聚焦系统有良好的特性。     

Intensity distribution of a capillary-discharge 46.9 nm soft X-ray laser

We realize a Ne-like Ar 46.9 nm soft X-ray laser pumped by a capillary discharge. The study of the laserpulse-intensity distribution is important for applications of soft X-ray lasers. The intensity distribution demonstrates the gain distribution, plasma radius, and axial plasma density that contribute to the study of the laser-pulse formation. To measure the intensity in different positions of the X-ray laser spot, we moved transversally an X-ray diode (XRD) assembled with a slit. We obtain the onedimensional intensity distribution. We find a laser divergence (FWHM) of 4.0 mrad. According to the gain-guided model, we calculate the intensity distribution. The measured divergence of 4.0 mrad roughly corresponds to a plasma radius a approximately equal to 230–250 μm and on-axis electron density n _e ≈ 8.0?10¹⁸ ?9.0?10¹⁸ cm ^?3. The results of calculations indicate that the divergence of the intensity distribution increases when the plasma radius decreases and the on-axis electron density increases.     

Recent results on development of a table-top soft X-ray laser

Gain measurements have been performed in a recombining carbon plasma generated by a line focussed Nd-glass laser beam on a multi-fin target with the aim of developing a table-top soft X-ray laser. With a laser beam of only 4 J (2ns) and a 6 mm long target gain up to 7.1 cm^–1 was measured for the C VI 18.2 nm line (gain-length 4.3). During these measurements high gain (6.5 cm^–1) was also measured for the first time on the C VI 13.5 nm line (4–2 transition). These measurements were done in the process of preparation for two-target experiments. High gain was measured independently for two separate, identical 6 mm targets. Changes in the influx into the plasma of iron ions from cooling blades significantly affected the location of the gain region and can be used as a mechanism to control the gain region in two-target experiments.     

强脉冲软X光辐照薄塑料闪烁体发光特性研究

介绍了Z-pinch实验用软X光功率仪的测量原理,利用“强光一号”产生的强脉冲软X光对薄塑料闪烁体(40 mm×0.1 mm)进行了辐照。实验中,采用两套软X光功率仪并安装在同一个大法兰面上,其中一套作为标准系统,参数保持不变,另一套系统的狭缝宽度逐渐增加,以改变软X光辐照到闪烁体上的能量通量密度。测量了软X光的辐射功率,由此计算得到在强脉冲软X光辐照下发光线性输出时能量通量密度下限,为1.47×105 W/cm2,为以后在Z-pinch物理诊断中合理安排探测系统提供了实验依据,使诊断结果更加合理和准确。     

Synchronized picosecond pulse generation with a synchronously pumped dye laser and a compressed Nd: YAG laser for non-degenerate transient grating experiments

We have set up a laser system which simultaneously provides synchronized picosecond pulses in the visible and at a wavelength of 1.06 m with a repetition rate of 76 MHz. The set-up consists of a dye laser synchronously pumped by the second harmonic of a cw mode-locked Nd:YAG laser and a fiber-grating compressor for the fundamental wavelength of the Nd;YAG laser. Crosscorrelation measurments reveal the time jitter between the two pulse trains to be less than 10 ps. As a first application we have performed non-degenerate transient grating experiments in semiconductors. The non-degenerate technique allows to use excitation energies well above the bandgap energy and to separate non-linear refractive index effects from photoinduced absorption or transmission changes.     

强脉冲软X光辐照薄塑料闪烁体发光特性研究

 介绍了Z-pinch实验用软X光功率仪的测量原理,利用“强光一号”产生的强脉冲软X光对薄塑料闪烁体(Ø40 mm×0.1 mm)进行了辐照。实验中,采用两套软X光功率仪并安装在同一个大法兰面上,其中一套作为标准系统,参数保持不变,另一套系统的狭缝宽度逐渐增加,以改变软X光辐照到闪烁体上的能量通量密度。测量了软X光的辐射功率,由此计算得到在强脉冲软X光辐照下发光线性输出时能量通量密度下限,为1.47×10⁵ W/cm²,为以后在Z-pinch物理诊断中合理安排探测系统提供了实验依据,使诊断结果更加合理和准确。     

A soft X-ray laser utilizing charge exchange

A scheme for a soft x-ray laser utilizing electron pickup in an excited state of a multiply ionized species is presented. Using a current source of 10 to 20 mA, we estimate a yield of ≈ 10⁶ x-ray quanta per pulse. The present scheme seems to be well within the realm of modern technology.     

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     

Beam-induced effects in soft X-ray photoelectron emission microscopy experiments

The beam-induced effects, a consequence of the high photon flux density used in soft X-ray photoelectron emission microscopes in operation at the 3rd generation synchrotron sources, are discussed and illustrated using some representative results obtained with the microscopes at the laboratory Elettra. The focus is on the photon-induced charge potential and chemical degradation, which might be a severe problem for photon-sensible specimens. The possible steps to avoid, reduce or even make use of the beam-induced effects are outlined.