Picosecond X-ray radiography of superdense high-temperature laser plasma

The layout of an X-ray source for diagnostics of the compressed state of laser plasma is proposed, and its optimal parameters are calculated under the conditions required for nuclear fusion. Such a source operating in a pulsed regime is intended to be used for determining the spatial distribution of laser-plasma density with high temporal resolution by means of multiframe (pulses follow with a specified time interval) backlight imaging of the main target by X-ray pulses obtained by irradiation of a secondary target by picosecond laser pulses.     

Expansion of matter heated by an ultrashort laser pulse

Recent experiments have utilizied high-power subpicosecond laser pulses to effect the ultrafast heating of a condensed material to temperatures far above the critical temperature. Using optical diagnostics it was established that a complicated density profile with sharp gradients, differing substantially from an ordinary rarefaction wave, forms in the expanding heated matter. The present letter is devoted to the analysis of the expansion of matter under the conditions of the experiments reported by D. von der Linde, K. Sokolowski-Tinten, and J. Bialkowski, Appl. Surf. Science 109/110, 1 (1996); K. Sokolowski-Tinten, J. Bialkowski, A. Cavalleri et al., Proc. Soc. Photo-Opt. Instum. Eng. 3343, 46 (1998); and, K. Sokolowski-Tinten, J. Bialkowski, A. Cavalleri et al., Phys. Rev. Lett. 81, 224 (1998). It is shown that if the unloading adiabat passes through the two-phase region, a thin liquid shell filled with low-density two-phase matter forms in the expanding material. The shell moves with a constant velocity. The velocity in the two-phase material is a linear function of the coordinate (flow with uniform deformation), and the density is independent of the coordinate and decreases with time as t ⁻¹. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 284–289 (25 February 1999)     

Heating of thin foils with a relativistic-intensity short-pulse laser

K-shell x-ray spectroscopy of sub-100 nm Al foils irradiated by high contrast, spatially uniform, 150 fs, Ilambda (2)=2 x 10(18) W microm(2)/cm(2), laser pulses is obtained with 500 fs time resolution. Two distinct phases occur: At /=500 fs the resonance transitions dominate. Initial satellites arise from a large area, high density, low temperature (approximately 100 eV) plasma created by fast electrons. Thus, contrary to predictions, a short, high intensity laser incident on a thin foil does not create a uniform, hot dense plasma.     

Lattice deformation from interaction with electrons heated by an ultrashort laser pulse

We propose a model describing the destruction of metals under ultrashort intense laser pulses when heated electrons affect the lattice through the direct electron-phonon interaction. The metal consists of hot electrons and a cool lattice. The lattice deformation is estimated immediately after the laser pulse up to the electron temperature relaxation time. The hot electrons are described with help of the Boltzmann and heat conduction equations. We use an equation of motion for the lattice displacements with the electron force included. Estimates of the lattice deformation show that the ablation regime can be achieved. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 195–199 (10 August 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

An accelerator scenario for a hard X-ray free electron laser combined with high energy electron radiography

In order to study the dynamic response of the material and the physical mechanism of fluid dynamics,an accelerator scenario which can be applied to both hard X-ray free electron laser and high energy electron radiography is proposed.This accelerator is mainly composed of a 12 GeV linac,an undulator branch and an eRad beamline.In order to characterize a sample's dynamic behavior in situ and real-time with XFEL and eRad simultaneously,the linac should be capable of accelerating the two kinds of beam within the same operation mode.Combining in-vacuum and tapering techniques,the undulator branch can produce more than 1011 photons per pulse in 0.1%bandwidth at42 keV.Finally,an eRad amplifying beamline with 1:10 ratio is proposed as an important complementary tool for the wider view field and density identification ability.     

The pumping of an X-ray laser by means of an optical laser

A new mechanism for pumping of an X-ray laser by an optical laser is suggested. The inverse population between the inner levels of atoms is attained by means of the use of fast laser plasma electrons.     

A proposal for an X-ray free-electron laser oscillator with an energy-recovery linac

We show that a free-electron laser oscillator generating x rays with wavelengths of about 1 A is feasible using ultralow emittance electron beams of a multi-GeV energy-recovery linac, combined with a low-loss crystal cavity. The device will produce x-ray pulses with 10{9} photons at a repetition rate of 1-100 MHz. The pulses are temporarily and transversely coherent, with a rms bandwidth of about 2 meV, and rms pulse length of about 1 ps.     

Front- and rear-face X-ray emission from laser-irradiated Al foils

Summary We studied theK-shell X-ray emission from plasmas produced by laser irradiation of Al foils. Electron temperature and density of the emitting region were estimated from line ratio measurements. Spectra obtained from the rear face of the foils showed that X-ray transmission is influenced by energy transport in the foil.     

Anomalous burn-through of thin foils by high-intensity laser radiation

The paper presents results of experiments performed on the Pico facility in which foils were heated by laser radiation, and anomalously fast burn-through of foils by a structured laser beam was detected. Comparison with two-dimensional calculations has allowed us to suggest a tentative mechanism for the effect under investigation. The targets in the experiments were thin aluminum foils of thickness 3 to 40 μm. The flux density of laser radiation on the target surface varied between 10¹³ and 10¹⁴ W/cm². We detected a strong dependence of the transmitted energy on the foil thickness and the shortening of the transmitted laser pulse. Penetration of laser radiation through foils with thicknesses considerably larger than 3 μm has been observed, although it was stated in earlier publications [V. V. Ivanov, A. K. Knyazev, A. V. Kutsenko, et al., Kratk. Soobshch. Fiz. FIAN No. 7–8, 37 (1997)]; A. é. Bugrov, I. N. Burdonskii, V. V. Gol’tsov et al., Zh. éksp. Teor. Fiz. 111, 903 (1997) [JETP 84, 903 (1997)] that, at the laser radiation parameters used in our experiment, the evaporated layer of the foil could not be thicker than 2 μm. Two-dimensional calculations have allowed us to interpret this effect in terms of local “piercing” of the target at spots on the target surface where the radiation intensity has its peaks. The possibility of reducing these peaks by using a symmetrizing prepulse is discussed in the paper. Zh. éksp. Teor. Fiz. 116, 1287–1299 (October 1999)     

射线检测数字实时成像的不一致性研究

在基于PaxScan4030平板探测器技术的射线检测中,输出图像的像质除受系统噪声的影响外,同时还受探测器固有的光电响应不一致性的影响。通过对影响平板探测器输出图像质量的分析,建立了探测器响应不一致性校正模型。在用常规叠加方法去除噪声的同时,利用校正因子对采集图像进行实时校正,以改善系统性能,提高成像质量。通过实验数据分析和对校正前后输出图像的比较,验证了此方法的可行性,从而为射线检测提供了一种有效的校正方法。     

Simulation of the expansion of a crystal heated by an ultrashort laser pulse

Molecular dynamics (MD) simulation of expansion of quickly heated Lennard-Jones (LJ) crystalline thin film is performed. The heating time is assumed to be much shorter than the characteristic expansion time. Such situation occurs when a femtosecond laser pulse is absorbed by a crystal. We established that plastic rarefaction wave is formed and propagates from the vacuum boundary into solid.     

Controlled transport and focusing of laser-accelerated protons with miniature magnetic devices

This Letter demonstrates the transporting and focusing of laser-accelerated 14 MeV protons by permanent magnet miniature quadrupole lenses providing field gradients of up to 500 T/m. The approach is highly reproducible and predictable, leading to a focal spot of (286 x 173) microm full width at half maximum 50 cm behind the source. It decouples the relativistic laser-proton acceleration from the beam transport, paving the way to optimize both separately. The collimation and the subsequent energy selection obtained are perfectly applicable for upcoming high-energy, high-repetition rate laser systems.     

Energy spectra of protons driven by ultra-short laser interaction with thin gold foils

在能量11 mJ、波长744 nm、脉宽120 fs、功率密度6×1016 W/cm2的超短脉冲装置上,开展了超短脉冲激光与2.1 μm和5.0μm金薄膜靶相互作用产生质子束的实验研究.利用Thomson谱仪测量了产生的质子能谱,发现利用2.1 μm金薄膜靶时,质子能谱由于质子源数量不足而在74 keV附近出现单能峰,5.0 μm的金薄膜靶产生的质子计数和能谱均比2.1 μm的金薄膜靶产生的低,主要原因是超热电子穿过薄膜靶时出现的能量损失和几何倾斜降低了电子回流所致.     

Optical properties of pulsed laser heated soot

To investigate the transient change of soot optical properties resulting from pulsed laser heating of soot in a cooled exhaust plume we have simultaneously performed cw light extinction at 405 and 830 nm and elastic light scattering at 1064 nm. A reversible increase to the 830-nm light extinction of up to 7%, observed during the time period where the soot was hot, suggests a temperature-dependent light absorption refractive index function, E(m _λ ). At low fluence, small permanent increases of E(m _λ ) of <2% were also observed. 405-nm extinction measurements revealed that the soot likely contained material which continued to absorb 405-nm radiation when desorbed, thus complicating measurement interpretation. 1064-nm light scattering measurements showed a gradual decrease of scattering propensity with increasing laser fluence up to the point of material loss, which is consistent with the expected decrease of the structure factor of the soot aggregates as they expand. It is concluded that variations of the optical properties are occurring at the time of laser-induced incandescence (LII) emission, which should be accounted for in time-resolved LII measurement interpretation.     

Dose-controlled irradiation of cancer cells with laser-accelerated proton pulses

Proton beams are a promising tool for the improvement of radiotherapy of cancer, and compact laser-driven proton radiation (LDPR) is discussed as an alternative to established large-scale technology facilitating wider clinical use. Yet, clinical use of LDPR requires substantial development in reliable beam generation and transport, but also in dosimetric protocols as well as validation in radiobiological studies. Here, we present the first dose-controlled direct comparison of the radiobiological effectiveness of intense proton pulses from a laser-driven accelerator with conventionally generated continuous proton beams, demonstrating a first milestone in translational research. Controlled dose delivery, precisely online and offline monitored for each out of ～4,000 pulses, resulted in an unprecedented relative dose uncertainty of below 10 %, using approaches scalable to the next translational step toward radiotherapy application.     

线状聚焦激光与金属作用的离子速度分布

本文报道了利用法拉第筒飞行时间法进行的离子测量.通过比较高功率激光线状聚焦和点状聚焦在平面金属靶上产生的离子发射特性,总结出离子速度分布和激光辐照密度的定标规律,以及离子速度分布的空间各向异性.实验是在上海光机所钕玻璃激光装置上进行的,激光束的波长为1.06μm,脉宽为300ps,辐照密度为10~(12)～10~(14)W/cm~2.     

X射线闪光照相杆箍缩二极管技术最新进展

 综合介绍了杆箍缩二极管的应用背景、工作原理和目前的研究概况,并阐述了目前较为典型的两种二极管,即真空杆箍缩二极管和等离子体填充杆箍缩二极管的性能。详细介绍了已经用于地下实验的Cygnus装置的运行参数和实验结果。最后分析了杆箍缩二极管在X射线闪光照相领域的发展前景。     

Preionization kinetics of an X-ray preionized XeCl gas discharge laser

The influence of preionization conditions on the performance of a XeCl gas discharge laser preionized by a short, high intensity x-ray pulse, has been studied. The laser output energy and optical pulse temporal characteristics have been used to determine the roles of initial electron density and of electron attachment to HCl and to impurities. Although the short pulse preionization technique functions well for XeCl when the laser voltage pulse has a short risetime (?20 ns), it is less well suited to XeCl lasers using slowly rising voltage pulses (>50 ns), or to F₂ containing gas mixtures (KrF and XeF lasers).     

High-pressure behaviour of an X-ray preionized discharge pumped XeCl laser

The output characteristics are described of an X-ray preionized discharge pumped XeCl laser, fed by a low-impedance pulse forming line (PFL), at pressures up to 12 bar. The influence of a multichannel rail gap placed between the PFL and the laser head on the output energy was studied. We found an increase of output energy with increasing pressure up to 8 bar. At higher pressures a saturation behaviour was found. The maximum output energy per unit volume was 6.5 J/l.     

Measurements of electron transport in foils irradiated with a picosecond time scale laser pulse

The heating of solid foils by a picosecond time scale laser pulse has been studied by using x-ray emission spectroscopy. The target material was plastic foil with a buried layer of a spectroscopic tracer material. The laser pulse length was either 0.5 or 2 ps, which resulted in a laser irradiance that varied over the range 10(16)-10(19) W/cm(2). Time-resolved measurements of the buried layer emission spectra using an ultrafast x-ray streak camera were used to infer the density and temperature conditions as a function of laser parameters and depth of the buried layer. Comparison of the data to different models of electron transport showed that they are consistent with a model of electron transport that predicts the bulk of the target heating is due to return currents.