Laser produced plasma

The need for high]y charged heavy ions from projected particle accelerators has recently led to a re-evaluation of the complex processes of ion production in laser generated plasmas. Possible mechanisms for the production of intense beams of high charge state ions are investigated as is the experimental evidence for these mechanisms. The hypothesis that 20 keV ions are driven by "hot electrons" is not supported by experimental work to date. This work, on the other hand, suggests that 30ps pulsation is the basic mechanism for the acceleration of tantalum ions up fo charge state 8-t-whose energy increases linearly with charge state up to 24keV. For long pulses and charge states between 8-}-and 18n u, it appears that there is a secondary mechanism of electron impact ionisation by plasma electrons of approximately 200 eV in the plasma in front of the target, resulting in ions whose energy of around 24 keV is independent of charge state.

Spectra of highly charged Mo ions generated in a laser-produced plasma were observed from 10 to 190 A with a 3 m grazing-incidence spectrograph. Line identifications in Moxxx-XXXII were made with the help of relativistic Hartree-Fock calculations. In Mo xxxi (Mg-like) the 3S2 1.SO-3 s 3p 'P, resonance line

HELIOS-CR is a user-oriented 1-D radiation-magnetohydrodynamics code to simulate the dynamic evolution of laser-produced plasmas and z-pinch plasmas. It includes an in-line collisionalradiative (CR) model for computing non-LTE atomic level populations at each time step of the hydrodynamics simulation. HELIOS-CR has been designed for ease of use, and is well-suited for experimentalists, as well as graduate and undergraduate student researchers. The energy equations employed include models for laser energy deposition, radiation from external sources, and high-current discharges. Radiative transport can be calculated using either a multi-frequency flux-limited diffusion model, or a multi-frequency, multi-angle short characteristics model. HELIOS-CR supports the use of SESAME equation of state (EOS) tables, PROPACEOS EOS/multi-group opacity data tables, and non-LTE plasma properties computed using the inline CR modeling. Time-, space-, and frequency-dependent results from HELIOS-CR calculations are readily displayed with the HydroPLOT graphics tool. In addition, the results of HELIOS simulations can be post-processed using the SPECT3D Imaging and Spectral Analysis Suite to generate images and spectra that can be directly compared with experimental measurements. The HELIOS-CR package runs on Windows, Linux, and Mac OSX platforms, and includes online documentation. We will discuss the major features of HELIOS-CR, and present example results from simulations.

Measurements of the total ion emission from a pair of colliding laser-produced aluminium plasmas were obtained with the aid of a Faraday cup detector. The energy profile width at half height of the kinetic energy distribution for ions emitted normal to the target was found to be 30% narrower for colliding plasmas compared with a single plasma. Similar to ion emission from single plumes, the mean ion kinetic energy is observed to increase with the energy of the incident laser pulse. However, the width of the ion energy distribution increases at a significantly slower rate than in the single plume case.

A flat-field grating XUV spectrograph has been set up for laser plasma interaction studies. It uses a variable groove-spacing concave grating !n grazing incidence geometry and operates in the wavelength range of 25-290 A. A brief description of the design principle, construction and operation is given. Variation of spectral resolution with respect to the position of detector plane is studied. A resolution of 0.2 A (at A = 35.0,~) observed from the emission spectrum of carbon plasma is in agreement with that expected from design considerations. The instrument facilitates recording of multiple spectra on a single film and can be coupled to a microchannel plate-CCD camera detection system for on-line monitoring and processing of the spectrum, and to an X-ray streak camera for temporally resolved spectral measurements.

The Engineering Test Stand (ETS) is a developmental lithography tool designed to demonstrate full-field EUV imaging and provide data for commercial-tool development. In the first phase of integration, currently in progress, the ETS is configured using a developmental projection system, while fabrication of an improved projection system proceeds in parallel. The optics in the second projection system have been fabricated to tighter specifications for improved resolution and reduced flare. The projection system is a 4-mirror, 4x-reduction, ring-field design having a numeral aperture of 0.1, which supports 70 nm resolution at a k 1 of 0.52. The illuminator produces 13.4 nm radiation from a laser-produced plasma, directs the radiation onto an arc-shaped field of view, and provides an effective fill factor at the pupil plane of 0.7. The ETS is designed for fullfield images in step-and-scan mode using vacuum-compatible, magnetically levitated, scanning stages. This paper describes system performance observed during the first phase of integration, including static resist images of 100 nm isolated and dense features.

This paper reviews recent experimental activity in the area of optimization, control, and application of laseraccelerated proton beams, carried out at the Rutherford Appleton Laboratory and the Laboratoire pour l'Utilisation des Lasers Intenses 100 TW facility in France. In particular, experiments have investigated the role of the scale length at the rear of the plasma in reducing target-normal-sheath-acceleration acceleration efficiency. Results match with recent theoretical predictions and provide information in view of the feasibility of proton fast-ignition applications. Experiments aiming to control the divergence of the proton beams have investigated the use of a laser-triggered microlens, which employs laser-driven transient electric fields in cylindrical geometry, enabling to focus the emitted protons and select monochromatic beamlets out of the broadspectrum beam. This approach could be advantageous in view of a variety of applications. The use of laser-driven protons as a particle probe for transient field detection has been developed and applied to a number of experimental conditions. this area has focused on the detection of large-scale self-generated magnetic fields in laser-produced plasmas and the investigation of fields associated to the propagation of relativistic electron both on the surface and in the bulk of targets irradiated by high-power laser pulses.

This article may be openly shared  because it is the work created by US government employee, and is considered to be in public domain according to an agreement between Elsevier and the US government. The US government is the copyright owner. The abstract follows: …. A prototype analyzer for the direct LIBS analysis of nebulized liquid samples was developed and tested, particularly for the analysis of petroleum, organic solvents and aqueous solutions. The LIBS analyzer requires about 750 μl of liquid sample, 1 l of N 2 gas, and 10 s of the analysis time to record 100 spectra. The limits of detection in oil and solvent are as low as 0.01-0.04 ppm for Li, Mg, and Cu. They increase for the difficult elements, such as Pb and Hg (7-10 ppm), Cl (250 ppm), and S (~0.7%). The relative standard deviation of measuring 100 ppm vanadium in oil and solvent was 1.5%. The LIBS detection limits and repeatability are better than required by the standard method ASTM D5185 for the analysis of lubricating oils in ICP-OES. Several petroleum samples were analyzed by LIBS and the quantitative results for V, Ni, and Fe compared to the ICP-OES data. Light crude oils can be nebulized and analyzed directly. Medium crude oils may require minimal dilution at least 1:1, otherwise errors of determination may become large. Presumably, utilization of the internal standard and chemometrics can be useful to correct for the matrix effects. In addition to the trace element analysis, the LIBS prototype demonstrated ability to measure the hydrogen-to-carbon ratio in organic liquid samples. Several unidentified features were observed in the carbon spectrum. Their possible origin is discussed. ☆ This article is published in a special honor issue dedicated to Richard E. Russo to commemorate his 70th. birthday, for his achievements in the fields of laser-material interaction, plasma modeling and evolution, surface analysis with lasers, and for his vision of what is needed and critical in future theoretical, instrumental and methodological development.

In this work, an aluminum laser plasma produced in ambient air at atmospheric pressure by laser pulses at a fluence of 10 J/cm 2 is characterized by time-and space-resolved measurements of electron density and temperature. Varying the laser pulse duration from 6 ns to 80 fs and the laser wavelength from ultraviolet to infrared only slightly influences the plasma properties. The temperature exhibits a slight decrease both at the plasma edge and close to the target surface. The electron density is found to be spatially homogeneous in the ablation plume during the first microsecond. Finally, the plasma expansion is in good agreement with the Sedov's model during the first 500 ns and it becomes subsonic, with respect to the velocity of sound in air, typically 1 As after the plasma creation. The physical interpretation of the experimental results is also discussed to the light of a one-dimensional fluid model which provides a good qualitative agreement with measurements. D

The electron density in a laser produced plasma experiment was measured utilizing the Stark broadening of the H α -line at 656.27 nm. This line results from the interaction of the Nd:YAG laser at the fundamental wavelength of 1.06 μm with a plane solid aluminum target in a humid air. The measurements were repeated at several delay times (0-10 μs) and at a fixed gate time of 1 μs. The electron density from the optically thin Al IIline at 281.62 nm was measured in parallel from the same spectra. The electron density was found in the range from 10 18 cm − 3 down to 6 × 10 16 cm − 3 at longer delay time. The electron density from the H α -line using the Griem's standard theory was compared with the predictions of other model due to Gigosos et al. The agreement between the measured electron density from both the H α -line and the Al II-line would confirm the reliability of utilizing the H α -line as an electron density standard reference line in LIBS experiments. Several important features characterize the H α -line: it is a well isolated line, it gives large signal to background ratio, it lasts a long time after the termination of the laser (up to 10 μs), its Stark width is relatively large and does not exhibit self-absorption.

A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic electric fields and double layers inside of plasmas including oscillations and damping. For the first time, a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laserproduced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitons and inverted layers, in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. We find the rotation of plasmas in magnetic fields and a new second harmonic resonance. Explanation of inverted double layers, second harmonic emission from laser-produced plasmas, and laser acceleration of charged particles by the very high fields of the double layers is given.

A partire dai pioneristici studi sui sistemi laser applicati alla diagnostica dei plasmi del gruppo di Ascoli Bartoli nei primissimi anni ’60 a Frascati, i laboratori del CNEN poi l’ENEA hanno sviluppato e mantenuto nei decenni competenze di assoluto livello internazionale nello sviluppo e nelle applicazioni di sistemi laser e più in generale di sorgenti di luce sia coerenti, sia incoerenti. Oggi, la compresenza nello stesso Centro di diverse sorgenti di luce che coprono una larghissima parte dello spettro delle onde elettromagnetiche (tutti ‘i colori’ a cui fa riferimento il titolo), dal THz ai raggi X duri, costituisce un caso unico in Italia di cui si parla poco ma che è una realtà scientifica e tecnologica acclarata da decenni. In questo articolo presentiamo un riassunto di alcune sorgenti di luce progettate e realizzate nel Centro ENEA di Frascati, e delle loro applicazioni in diversi campi scientifici e tecnologici.

The article shows that the application of the technological scheme of laser-plasma cutting and welding with coaxial summing of both energy sources on one side of the workpiece leads to the appearance of the so-called hybrid effect, which consists in "binding" the anode spot of the arc to the radiation zone, stabilizing its combustion in the hybrid process at currents up to 300 A and reducing the voltage at the arc gap due to the increase of its electrical conductivity due to overheating of the plasma by laser radiation, this allows to significantly increase the speed of cutting and welding processes without increasing the running energy. The use of technological schemes of laser-plasma cutting and welding with an inclined arrangement of both components of the hybrid process, supplied from one side of the workpiece, also leads to a hybrid effect, but it can be less pronounced, and there is a risk of damage to parts of the equipment (for example, optical elements) reflected from the working area radiation.

We report measurements of the temporal and spatial evolution of plasmas, produced on gaseous targets by focused ns-Nd:YAG laser. Characterization of the UV-VUV light source includes time-resolved visualization of the spatial growth and the spectroscopic signatures of plasmas produced on pulsed, supersonic jets of helium, argon, nitrogen and xenon gases into a vacuum chamber. Photon fluxes of up to 10 12 photons cm À2 nm À1 /pulse have been measured in the wavelength region 100-260 nm within the first 30 ns following the laser pulse. Also discussed for comparison are plasma signatures in helium, argon and nitrogen gases at standard temperature and pressure.

A theoretical model for nanosecond laser ablation at 1064 nm of quaternary bronze alloys containing Cu, Sn, Zn and Pb was developed. Starting from a known sample composition, the model provides the element concentrations in the laser produced plasma, and therefore the plasma stoichiometry, here studied for different laser energies on the target. For the considered laser excitation, plasma stoichiometry cannot be achieved in the ablation of bronze materials; however, stable element ratios in the plasma occur for a laser fluence above 600 J/cm 2 , corresponding to an irradiance of 75 GW/cm 2 . The calculated plasma concentrations were then used to simulate calibration plots in the range of element concentrations corresponding to the standards available. Different kinds of internal standardization were theoretically considered and successively applied to the experimental data obtained. Good agreement between experimental results and model predictions was observed, allowing establishing the optimal method for LIBS calibration of bronze alloys. Further validation of the model was attempted by comparing the predicted element concentrations in the plasma with the experimental results obtained by using the Calibration-Free (CF) approach (Corsi et al., Eur.Phys.J. D13, 2001, 373). The results obtained are in excellent agreement between themselves. However, the estimated element concentrations largely differ from those in samples, and the reasons for the discrepancy are discussed. D

The paper describes a debris-free, efficient laser-produced plasma source emitting EUV radiation. The source is based on a double-stream Xe/He gas-puff. Its properties and spectroscopic signatures are characterized and discussed. The spatio-spectral features of the EUV emission are investigated. We show a large body of results related to the intensity and brightness of the EUV emission, its spatial, temporal, and angular behavior and the effect of the repetition rate as well. A conversion efficiency of laser energy into EUV in-band energy at 13.5 nm of 0.42% has been gained. The electron temperature and electron density of the source were estimated by means of a novel method using the FLY code. The experimental data and the Hullac code calculations are compared and discussed. The source is well suited for EUV metrology purposes. The potential of the source for application in EUV lithography was earlier demonstrated in the optical characterization of Mo/Si multi-layer mirrors and photo-etching of polymers.

Absh.act-Results of measurements of longitudinally-averaged vibrational and rotational temperatures of CO2 for different radial positions in the active medium of a fast-axial-flow, dcexcited CO2 laser are reported. The diagnostic technique which was implemented is high resolution absorption spectroscopy of the laser plasma, using a tunable diode laser (TDL). Two different gas inlet sections for the CO2 laser were tested: One with a single anode pin in front of a relatively large inlet nozzle, as still commonly used in industrial high-power lasers, and another with multiple anodes symmetrically spaced around the perimeter of the discharge tube, each in front of a small diameter inlet nozzle. It is shown that the latter design is capable of creating an essentially flat profile regarding rotational temperature TR and combined bending mode (Tz) and symmetric stretch mode (TI % Tz) temperature, while the asymmetric stretch temperature T3 exhibits a small central maximum. This type of gain pattern is considered to be beneficial for mode quality. The former, mostly used gas inlet design, fails to provide an adequate gain profile (i.e., flat or centered and symmetrical). The combination of the information provided by the spectroscopic technique and a previously developed theoretical model can prove to be a real design aid for developing compact, high-power, gaussian mode CO2 lasers for materials processing applications.

The industrial aluminum reduction cell is an electrochemistry reactor that operates under high temperatures and corrosive conditions. Monitoring the molten aluminum and electrolyte components is very important for controlling the chemical reaction process. Due to the lack of fast methods to monitor the components, controlling aluminum reduction cells is difficult. In this work, laser-induced breakdown spectroscopy (LIBS) was applied to aluminum electrolysis. A new method for calculating the molecular ratio, which is an important control parameter that represents the acidity of the electrolyte, was proposed. Experiments were first performed on solid electrolyte samples to test the performance of the proposed method. Using this method, the average relative standard deviation (RSD) of the molecular ratio measurement was 0.39%, and the average root mean square error (RMSE) was 0.0236. These results prove that LIBS can accurately measure the molecular ratio. Then, in situ measurements of the molten aluminum and electrolyte were performed in industrial aluminum induction cells using the developed LIBS equipment. The spectra of the molten electrolyte were successfully obtained and were consistent with the spectra of the solid electrolyte.

Starting from the experimental results of generation of ions from plasmas driven by the laser-facilityHercules at ENEA Frascati, we present some basic equations that account for the main physical phenomena occurring during the plasma expansion from the laser target, including the cluster expansion dynamics.

We have developed compact, high repetition, table-top soft-X-ray sources, based on a gas puff target, emitting in ''water window" spectral range at k = 2.88 nm from nitrogen gas target or, in 2-4 nm range of wavelengths, from argon gas target. Double stream gas puff target was pumped optically by commercial Nd:YAG laser, energy 0.74 J, pulse time duration 4 ns. Spatial distribution of laser-produced plasma was imaged using a pinhole camera. Using transmission grating spectrometer, argon and nitrogen emission spectra were obtained, showing strong emission in the ''water window" spectral range. Using AXUV100 detector the flux measurements of the soft-X-ray pulses were carried out and are presented.

It is a well-known fact that laser-induced breakdown spectroscopy (LIBS) has emerged as one of the best analytical techniques for multi-elemental compositional analysis of samples. We report assembling and optimization of LIBS set up using high resolution and broad-range echelle spectrograph coupled to an intensified charge coupled device (ICCD) to detect and quantify trace elements in environmental and clinical samples. Effects of variations of experimental parameters on spectroscopy signals of copper and brass are reported. Preliminary results of some plasma diagnostic calculations using recorded time-resolved optical emission signals are also reported for brass samples.

Two-electron satellite transitions near He ÿ , 1s2s3s-1s 2 2p and 1s2s3d-1s 2 2p, have been identiÿed in dense laser-produced plasmas. Space resolved high-resolution spectra indicate that their existence is conÿned to the area of the laser spot thereby providing a localized emission source of the highest density plasma region. Detailed modeling with the MARIA-code veriÿes their advantageous use as diagnostic reference lines in dense optically thick plasmas. Close to the target surface, anomalous high emission is encountered for the Li-like two-electron transitions op = 1s2s 2 -1s 2 2p. The high resolution data taken with spherically bent mica crystals indicates that there is an intensity correlation with higher order intercombination satellite transitions 1s2l3l -1s 2 2l near He . An important ÿnding is the very good agreement between the data and the simulations, when considering forbidden transitions only and when using two-electron transitions as reference lines. Based on these reference lines space resolved non-Maxwellian signatures could be determined. ?

Shot-to-shot variation in the characteristics of laser produced plasma plume and surface profile of N-type silicon (1 1 1) are investigated. In order to produce plasma, a Q-switched Nd: YAG laser (1064 nm, 10 mJ, 9-14 ns) is tightly focused on silicon target in air at room temperature. Target was exposed in such a way that number of laser shots was increased from point to point in ascending order starting from single shot at first point. Target was moved 2 mm after each exposure. In order to investigate shot-to-shot variation in the time integrated emission intensity regions within the plasma plume, a computer controlled CCD based image capture system was employed. Various intensity regimes were found depending strongly on the number of incident laser pulses. Plasma plume length was also found to vary with the number of pulses. The topographic analysis of the irradiated Si was performed by Scanning Electron Microscope (SEM) which shows the primary mechanisms like thermal or non-thermal ablation depend on the number of shots. Surface morphological changes were also studied in terms of ripple formation, ejection, debris and re-deposition of material caused by laser beam at sample surface. The micrographs show ripples spacing versus wavelength dependence rule [K % k/(1 À sin h)]. Intensity variations with number of shots are correlated with the surface morphology of the irradiated sample.

The possibility of using high-intensity laser-produced plasmas as a source of energetic ions for heavy ion accelerators is addressed. Experiments have shown that neon ions greater than 6 MeV can be produced from gas jet plasmas, and well-collimated proton beams greater than 20 MeV have been produced from highintensity laser solid interactions. The proton beams from the back of thin targets appear to be more collimated and reproducible than are high-energy ions generated in the ablated plasma at the front of the target and may be more suitable for ion injection applications. Lead ions have been produced at energies up to 430 MeV.

New types of space resolved X-ray spectra produced in light matter experiments with high intensity lasers have been investigated experimentally and theoretically. This type of spectra is characterised by the disappearance of distinct resonance line emission and the appearance of very broad emission structures due to the dielectronic satellite transitions associated to the resonance lines. Atomic data calculations have shown, that rather  exotic states with K-shell vacancies are involved. For quantitative spectra interpretation we developed a model for dielectronic satellite accumulation (DSA-model) in cold dense optically thick plasmas which are tested by rigorous comparison with space resolved spectra from ns-lasers. In experiments with laser intensities up to 1019 W/cm2 focused into nitrogen gas targets, hollow ion configurations are observed by means of soft X-ray spectroscopy. It is shown that transitions in hollow ions can be used for plasma diagnostic. The determination of the electron temperature in the long lasting recombining regime is demonstrated. In Light-matter interaction experiments with extremely high contrast (up to 10^10) short pulse (400 fs) lasers electron densities of ne≈3×10^23cm^−3 at temperatures between kTe=200–300 eV have been determined by means of spectral simulations developed previously for ns-laser produced plasmas. Expansion velocities are determined analysing asymmetric optically thick line emission. Further, the results are checked by observing the spectral windows involving the region about the Heα-line and the region from the Heβ-line to the He-like continuum. Finally, plasmas of solid density are characteristic in experiments with heavy ion beams heating massive targets.
We report the first spectroscopic investigations in plasmas of this type with results on solid neon heated by Ar-ions. A spectroscopic method for the determination of the electron temperature in extreme optically thick plasmas is developed.
1. Introduction
The investigation of dense plasma has received great interest in a widespread community: inertial fusion driven by lasers and heavy ion beams, X-ray lasers, non-coherent X-ray sources, and correlation effects in dense cold plasmas. In these investigations plasma spectroscopy has provided important information for basic research and for the optimisation of desired plasma parameters. X-ray spectroscopy of these dense plasmas, which contain highly charged ions, has turned out to be extremely useful for the determination of the plasma parameters and several models have been successfully developed in the last decades, e.g. see [1] and [2]. The general feature of these traditional spectra are the dominant emission of resonance lines.

Recently, the interaction of radiation with matter by means of powerful lasers with extremely high contrast of up to 1011 produce spectra which differ dramatically from traditional ones, e.g. known from ns-laser experiments. A general feature of these newer spectra is the disappearance of the resonance lines and the appearance of very broad emission structures associated to the resonance lines. Theoretical calculations readily showed that neither Stark-broadening nor opacity effects could account for the experimental observation. Only recently, Rosmej and Faenov [3] proposed a model of accumulated dielectronic satellites (DSA-model) for the interpretation of the experimental findings [4], [5], [6], [7] and [8].

It became immediately clear that spectra from short pulse high-power high-contrast lasers were not appropriate to study the origins of the observed spectra. Transient effects, field ionisation, continuum level depression at high densities and optical thickness made the theoretical interpretation difficult. Therefore, it was appropriate to perform experiments that could illuminate the situation and perform systematic investigations at ns-laser installation. The keypoint in these experiments being the measurement of X-ray spectra with high luminosity at high spectral and spatial resolution. This was realised by means of spherically bent mica crystals providing a spectral resolution of λ/δλ≈104 simultaneously with spatial resolution of m [9], [10] and [11]. Note that spectra emitted from plasmas in traditional ns-laser experiments arising from regions close to the target surface showed emission features similar to those known from high-intensity high-contrast laser pulses.

Not all questions could be addressed in these experiments, in particular the broad emission structures located far from usual resonance line positions [12], [13] and [14] required further study. A major step the atomic data calculations that showed these structures might be due to transitions in hollow ions [7], [8], [14], [15] and [16]. However, the question concerning the excitation mechanisms however remained unresolved.

The similarity of cold, dense plasmas created by short pulse high-contrast lasers and plasmas generated through heating solids with heavy ion beams made the beam–solid interaction experiments attractive to the laser community. Spectroscopic investigations of the first experiments with Ar-ions heating solid neon [17] were thus pursued.

2. Laser produced plasmas
2.1. Observation of unusual X-ray spectra from high-intensity high-contrast laser pulses
Experiments on the interaction of high-intensity high-contrast lasers with solid targets have been performed at the Centre for Ultrafast Optical Science of the University of Michigan [18] and [19]. The pulse had a duration of 400 fs, a wavelength of m, an energy of 1 J, and an intensity contrast of 1010. The diameter of the focal spot was about m and a peak intensity of 0.5×1019 W/cm2 was achieved at the surface of a solid target. In addition, experiments with prepulses were performed with a total energy of 2 J and a time separation from the main pulse of 2 ps. Solid Mg targets were used. X-ray spectra [19] have been recorded with spherically bent mica crystals with a 186 mm radius of curvature and X-ray CCD camera. The geometrical arrangement uses the FSSR-1D scheme [10].

A large-volume non-conventional XeCl excimer laser (Hercules) emitting long pulses (from 10 ns up to 120 ns at a wavelength of 308 nm) has been used to drive a soft X-ray plasma source. The X-rays pulse duration and the energy conversion efficiency in different spectral regions have been measured; X-rays emission lasting up to 100 ns has been obtained in the 70 eV region. The dependence of X-ray pulse duration on the size of the laser spot is  discussed. The X-ray source can be operated both in vacuum and in helium at atmospheric pressure. This allows irradiating over a large area both for contact microscopy of living specimens (up to 1 mm^2 windows) and for radiobiology (up to few cm^2 windows). The experimental results obtained for these two applications as well as for radiographic images of living insects are discussed.

Extreme ultraviolet (EUV) radiation with wavelengths of 11-14 nm is seen as the most promising candidate for a new lithographic technology. Compared with synchrotron radiation sources and laser-produced plasmas, gas dischargeproduced plasma sources for EUV radiation are expected to offer lower cost of ownership. Using xenon, a broadband emission in the investigated wavelength range from 10 to 17 nm is observed. Very short current pulses, having a fast rise time of 85-or 140-ns duration and 23-kA amplitude, were applied across the xenon-filled Z-pinch capillary (3-mm diameter and 5-mm length) to produce EUV radiation. An EUV radiation from the Z-pinch plasma was characterized, which is based on the temporal behavior of EUV intensity and the pinhole images. Two maximum EUV radiations occur, which are sensitive to the xenon flow rate and the discharge current. The first radiation is relatively of short duration, while the second radiation lasts as long as the first period of the current flows. The EUV source size due to the first radiation is approximately 300 µm, i.e., half of the one due to the second radiation.

The possibility to excite low-energy nuclear states using laser induced plasma on the Prague Asterix Laser System PALS is investigated. This medium-energy high-power facility yields interaction intensities at the level of 10 16 ÷ 10 17 Wcm −2 thus producing subrelativistic plasmas with electron temperature of the order of 1 ÷ 10 keV. Based on a systematic survey of suitable candidate nuclei, the search for the 6.238 keV excitation and decay in 181 Ta has been initiated. Tests and preliminary operation of detecting systems including active detectors are reported.

Conversion efficiency of a laser-produced Sn plasma at 13.5 nm, simulated with a one-dimensional hydrodynamic model and treated as a multi-component blackbody A Cummings, G O'Sullivan, P Dunne, E Sokell, N Murphy and J White 2005 J. Phys. D: Appl. Phys. 38 604-16 Due to a misinterpretation of the solid angle involved in the collection of the 2% bandwidth (BW) EUV radiation at 13.5 nm, the net power output of figures 8 and 9 are in actual fact given with respect to 4π sr and not 2π sr. Thus our previous results for the conversion efficiencies (CEs) within figure 10 are for 4π sr. This gives optimum CEs, for the given target geometry and illumination conditions, of 1.75-3% into the 2% BW at 13.5 nm per collectable solid angle of 2π sr. These predicted CEs are now more in line with the quoted experimental values of [28] and [52, 53] and still support the main contention of our study that 3% CEs should be/are attainable with the utilization of a laser-produced Sn plasma source. Also, now attains a maximum of 0.74% into the 2% BW per collectable solid angle of 2π sr at a temperature of 23.4 eV.

A detailed analysis of the x-ray spectrum emitted by laser-produced plasma of samarium (6-12 Å) is presented, using ab initio calculations with the HULLAC relativistic code and isoelectronic considerations. Resonance 3d-nf (n =4 to 7), 3p-4d, 3d-4p, and 3p-4s transitions in Ni samarium ions and in neighboring ionization states (from Mn to Zn ions) were identified. The experiment results show changes in the fine details of the plasma spectrum for different laser intensities.

Laser ablation is widely used to assist in the fabrication of prototype lithium manganate (LiMn 2 O 4 ) thin film structures for Li-ion battery electrodes via the pulsed laser deposition technique. However, films can be considerably Li and/or O deficient, depending the deposition conditions used. Here we present data on the ionic component of laser-produced plasma in laser ablation of lithium manganate with ns excimer laser. Plasma was monitored using an electrical Langmuir ion probe, in time-of-flight mode in conjunction with mass spectrometry to identify the dominant ionic species. Ablation in vacuum at $2.5 J cm À2 revealed the plasma's ionic component was composed primarily of singly charged Li and Mn ions. The time-of-flight data indicates significant deceleration of the plasma when ablation is carried out in an oxygen background gas pressure of the order of 10 Pa. The implications for thin film growth are considered in terms of the possible gas phase interactions and/or thin film re-sputtering yield. #

We have found that the divergence of a relatively monochromatic extreme ultraviolet ͑EUV͒ emission from a laser-produced plasma can be manipulated by changing the target morphology which is a porous low-density tin oxide ͑SnO 2 ͒ structure. The fundamental light of a Nd-YAG laser was irradiated on the target with laser intensity of ϳ10 11 W/cm 2 and pulse duration of 10 ns. The nanostructure and density of the targets were tuned by a combination of colloidal polymer template and sol-gel processes ͓Gu, Nagai, Norimatsu, Fujioka, Nishimura, Nishihara, Miyanaga, and Izawa, Chem. Mater. 17, 1115 ͑2005͔͒, which has a merit in large-scale preparation. When the target has an open cell nanostructure, the EUV emission directed predominantly along target normal, while a closed cell target exhibited divergent emission. The angular distribution may be affected by the orientation of the microstructured initial target, and this phenomenon can be applied to wavefront control of EUV emission.

By means of spatially resolved high-resolution X-ray spectroscopy, we have investigated the generation of fast ions at various laser installations with different flux densities and laser wavelengths. It is demonstrated that the fast ion generation in laser-produced plasma can be achieved for a very low level of the averaged laser intensity on the target. The time-of-flight mass spectrometry ion diagnostics and X-ray spectrographs give very close results for the energy distribution of the thermal ion component. For higher energies, however, we found significant differences: the spatially resolved high-resolution spectrographs expose the presence of suprathermal ions, while the time-of-flight method does not. Suprathermal ion energies plotted as a function of the qλ2 parameter show a large scatter far above the experimental errors. The cause of these large scatters is attributed to a strong non-uniformity of the laser intensity distribution in the focal spot. The analysis by means of hydrodynamics and spectral simulations show that the X-ray emission spectrum is a complex convolution from different parts of the plasma with strongly different electron density and temperature. It is shown that the highly resolved Li-like satellite spectrum near Heα contains significant distortions even for very low hot electron fractions. Non-Maxwellian spectroscopy allows determination of both the hot electron fraction and the bulk electron temperature.

The first Italian Micro Exposure Tool (MET) for EUV lithography has been developed at the ENEA Research Laboratories in Frascati. This tool (named MET-EGERIA) is based on a laser-plasma EUV source (named EGERIA), a couple of twin grazing-incidence collectors and a nonconventional Schwarzschild optics. In spite of the very low cost of the Schwarzschild optics, the specific design of the low vibration board and the innovative alignment technique (a modified Foucault technique) applied to the Schwarzschild optics allowed the achievement of a resolution better than 100 nm on a wafer coated with a PMMA photoresist. The MET-EGERIA is also suitable for the coloration of lithium fluoride to be used in photonics, and is also a promising tool for nanobiotechnological research.

The industrial aluminum reduction cell is an electrochemistry reactor that operates under high temperatures and corrosive conditions. Monitoring the molten aluminum and electrolyte components is very important for controlling the chemical reaction process. Due to the lack of fast methods to monitor the components, controlling aluminum reduction cells is difficult. In this work, laser-induced breakdown spectroscopy (LIBS) was applied to aluminum electrolysis. A new method for calculating the molecular ratio, which is an important control parameter that represents the acidity of the electrolyte, was proposed. Experiments were first performed on solid electrolyte samples to test the performance of the proposed method. Using this method, the average relative standard deviation (RSD) of the molecular ratio measurement was 0.39%, and the average root mean square error (RMSE) was 0.0236. These results prove that LIBS can accurately measure the molecular ratio. Then, in situ measurements of the molten aluminum and electrolyte were performed in industrial aluminum induction cells using the developed LIBS equipment. The spectra of the molten electrolyte were successfully obtained and were consistent with the spectra of the solid electrolyte.

We present a low-cost microexposure tool for projection lithography at 14.4 nm we have designed and operated at the ENEA Research Centre, Frascati. It is a laboratory-scale system based on a Schwarzschild-type projection optics which uses a laser-plasma soft X-ray source, equipped with a patented debris mitigation system in order to preserve the collector optics. As a preliminary result, we achieved a 90-nm optical resolution patterning on commercial resist. A sharp improvement in resolution size is expected when operating this tool by a large-output energy excimer laser in order to obtain a single-shot patterning.