Search

The laser surface modifications of a bulk material Inconel 600 and a multilayered titanium-aluminium-nitride/titanium-nitride(TiAlN/TiN) coating are of great interest for fundamental and practical aspects.Observation of surface changes of the Inconel 600 and TiAlN/TiN induced by ultra-short(fs and ps) and short(ns) lasers is considered.It is shown that all laser systems can stimulate morphological changes at the target surface,and the irradiation with ultra-short pulses results in a better definition of the damage.Fs laser pulses can produce a sharper destruction in comparison to the ps pulses and it gives the conical cross section of the crater,which is in contrast to the semispherical shapes ps laser beams.Furthermore,thermal effects are dominant in the case of ns pulse,and all irradiations are accompanied by the plasma.

The advance in laser plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular the upcoming experiments with the FLAME laser at LNF will enter the GeV regime with almost 1pC of electrons. From the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need to develop a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV) under still unknown angular divergences. Within the PlasmonX experiment at LNF a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence present unprecedented challenges in the design and construction of such a device. We will present the design considerations for this spectrometer and the first results from a prototype., Comment: 7 pages, 6 figures, submitted to NIM A

High power laser science and engineering 9, e3 (2021). doi:10.1017/hpl.2020.38, In this work we present experimental results on the behavior of diamond at megabar pressure. The experiment was performed using the PHELIX facility at GSI in Germany to launch a planar shock into solid multi-layered diamond samples. The target design allows shock velocity in diamond and in two metal layers to be measured as well as the free surface velocity after shock breakout. As diagnostics, we used two velocity interferometry systems for any reflector (VISARs). Our measurements show that for the pressures obtained in diamond (between 3 and 9 Mbar), the propagation of the shock induces a reflecting state of the material. Finally, the experimental results are compared with hydrodynamical simulations in which we used different equations of state, showing compatibility with dedicated SESAME tables for diamond., Published by Cambridge Univ. Press, Cambridge

A study of the surface modification of titanium CP grade 2 implant/target with high intensity picosecond (Nd:YAG) laser, operating at 1064 nm wavelength and pulse duration of 40 ps, in gaseous (air) and liquid (water) medium, is presented. The exposure of Ti to a laser pulse energy of 17 mJ in both media - gaseous and liquid, induced specific surface features and phenomena: (i) enhancement of the implant surface roughness (higher in water). In this context, the damage depth is more prominent in water (as high as 40 mu m) vs. air (similar to 14 mu m). Also, the appearance of laser induced periodic surface structures (LIPSS) is recorded in both media, at periphery area, while in water they are registered at lower pulse count; (ii) variation of chemical surface content depending on the applied medium. Thus, in the central irradiation region, the oxygen was absent in air while its concentration was relatively high (6.44 wt%) in case of water; (iii) possibility of direct collection of synthesized titanium based nanoparticles in water environment, and (iv) formation of the plasma above the sample in both mediums, more volumetrically confined in water. These investigations showed that surface structuring and observed phenomena are in strong correlation with the medium used. The liquid - water seems like the medium of choice in regard to titanium implant biocompatibility and bio-activity (the water is a favorable medium for build-up of the oxide layer which affects bioactivity). The process of laser interaction with titanium implant targets was accompanied by the formation of plasma plume, which provides the additional sterilizing effect facilitating contaminant-free conditions. (C) 2017 Elsevier B.V. All rights reserved.

International audience; This work presents an innovative usage of the GEMpix detector for soft X-rays (SXR) measurements aimed to make an estimate of the electron temperature of a Laser Produced Plasma (LPP). The GEMpix is a proportional gas detector based on three Gas Electron Multipliers (GEMs) with a Front-End Electronics (FEE) based on four Timepix chips. This FEE provides the Time over Threshold (ToT) acquisition mode pixel by pixel and then a digital measure of the released charge in the gas mixture. In addition, the charge can be amplified through the GEM foils with 4 orders of magnitude spanning gain offering, in this way, a big dynamic range and adjustable sensitivity. Chip design provides a threshold for each channel. All the thresholds are set in order to cut electronic noise and detect X-rays. In this configuration, a cut on the low amplitude signals is set, but the gain has been tuned in order to observe the main signal due to the soft X-rays reaching the detector. This detector works in an energy range between 2 to 15 keV . It offers good imaging properties, high efficiency and absolute calibration. It offers a good immunity to Electromagnetic Pulse (EMP), as checked at VEGA-2 laser facility (hundreds of TW in about 30 fs). In these experiments, where the formation of warm dense matter produced by blast waves has been studied, a measure of the plasma temperature was required. This measurement was realized applying some filters on the active area of the detector, in correspondence of three chips. With this configuration a study of the GEMpix response due to the photons coming from the coronal plasma produced by the laser on the target has been done for each single shot. GEMpix revealed innovative and attractive features, compared to the state of the art where passive films or detectors based on indirect conversion are used, for SXR imaging and spectral analysis to infer the electron temperature.

We have analyzed the laser driven shock behavior in experiments with double focal spots, in particular, its cumulative effect in double layer foam-metal targets, explained by multiple collisions of individual shocks in the structured target. Some of experimental shock dynamics results are in a good agreement with the theoretical and numerical predictions, but others demand for new models.

We studied the interaction of a double-spot laser beam with targets using the Prague Asterix Laser System (PALS) iodine laser working at 0.44 μm wavelength and intensity of about 1015 W/cm2. Shock breakout signals were recorder using time-resolved self-emission from target rear side of irradiated targets. We compared the behavior of pure Al targets and of targets with a foam layer on the laser side. Results have been simulated using hydrodynamic numerical codes.

In this work, we describe the results of experiments performed at the femtosecond ECLIPSE laser facility at CELIA in Bordeaux. We irradiated targets constituted by aluminum foils of various thicknesses and characterized the accelerated protons with energies in the range of interest for p+11B nuclear fusion. Time-of-flight measurements were performed by using Chemical Vapor Deposition (CVD) monocrystalline diamond detectors, which are specifically designed to operate in harsh environments where large ElectroMagnetic Pulses (EMPs) are generated during laser-target interaction. The 1 Hz high repetition rate used for the ECLIPSE laser allowed the collection of a large number of similar shots, giving therefore a large statistics to accurately characterize the energy spectrum of the laser-plasma accelerated protons. The laser repetitivity at a relatively small intensity permits to improve the signal-to-noise ratio of the detection of the products of low cross-section reactions, such as the p+11B one, by their collection over a large number of similar shots.

During the last 10 years of research it has been experimentally demonstrated that ions can be accelerated up to energies of tens of MeV as a consequence of the ultra-intense laser pulse interaction with a solid target. This process has been shown to take place via the so-called Target Normal Sheath Acceleration (TNSA) mechanism. A fundamental challenge in the investigation of this phenomenon is to understand the dependencies of the ion beam features on the laser and target properties. In order to achieve this goal, several TNSA theoretical models have been proposed. In the present work a collection of maximum ion energies experimentally measured has been compared to the values predicted by six different theoretical descriptions. The models we chose to compare are based either on a fluid approach, on a quasi-static approach, or on a combination of the before-mentioned. On the basis of such a quantitative comparison we aim to provide a reliable test of these theoretical descriptions, in which their strengths, weaknesses, open problems and capability in predicting the ion energy are underlined. © 2011 Elsevier B.V.

In this paper we report the results of experiments on LIFT performed using single pulses from a mode locked (40ps pulses), frequency doubled Nd:YAG laser (energy flux ≈ 13J/cm at λ = 532 nm). We studied the controlled transfer of thin films of different metallic materials to a receiving substrate. Optical and scanning electron microscopy (SEM) as well as Energy-dispersive X-ray spectroscopy (EDAX) analysis were performed, showing evidence of the production of micrometric scale patterns. One of our objectives is to investigate and develop possible applications of LIFT in jewellery industry. In order to understand the experimental results we developed a simple analytical model based on the Rankine-Hugoniot relations. Comparison between experimental and simulated results is presented. DOI:10.2961/jlmn.2011.02.0010

A 250-TW laser system (FLAME - Frascati laser for acceleration and multidisciplinary experiments) is now in its commissioning phase in a new laboratory at LNF-INFN in the framework of the PLASMONX (Plasma acceleration and monochromatic X-ray generation) project. The laser will deliver < 25 fs duration pulses with an energy up to 6J, at a 10Hz repetition rate. An ad hoc target area has also been designed and is currently being set up, allowing the first test experiments of electron laser wakefield acceleration to be carried out over the next few months in a safe, radiation-protected environment. An overview of the main features of the laser system and target area is given, along with a survey of the design and set-up of the self-injection test experiment, which is expected to reach the production of sub-GeV electron bunches. © 2010 Taylor and Francis.

In this paper, we describe the experimental validation of the technique of correction of wavefront aberration in the middle of the laser amplifying chain. This technique allows the correction of the aberrations from the first part of the laser system, and the pre-compensation of the aberrations built in the second part. This approach will allow an effective aberration management in the laser chain, to protect the optical surfaces and optimize performances, and is the only possible approach for multi-petawatt laser system from the technical and economical point of view. This approach is now possible after the introduction of new deformable mirrors with lower static aberrations and higher dynamic than the standard devices.

We present a series of experimental results, and their interpretation, connected to various aspects of the hydrodynamics of laser produced plasmas. Experiments were performed using the Prague PALS iodine laser working at 0.44 μm wavelength and irradiances up to a few 1014W/cm2. By adopting large focal spots and smoothed laser beams, the lateral energy transport and lateral expansion have been avoided. Therefore we could reach a quasi one-dimensional regime for which experimental results can be more easily and properly compared to available analytical models.

The use of the Soft X-ray Contact Microscopy technique is discussed as a possible new tool to get information on dopant distribution in the core of single-mode optical fibers with 50 nm spatial resolution.

In this paper the results of an experiment on soft X-ray contact microscopy using a laser-plasma source are presented. A resolution of 50 nm has been achieved imaging pig sperm cells, while other specimens, such as algae and yeast cells, showed internal details, proving the technique to be a powerful tool for biological investigations. Original biological information has been obtained and the conditions for optimal image formation have been studied.

A new design for targets employed in laser induced shock-compression experiments is presented. Numerical simulations to optimize target parameters and to clarify shock dynamics are realized. The experiments proved the new scheme is reliable and appropriate for reflectivity measurements of thermodynamical states lying out of the standard graphite or diamond Hugoniot: the final state reached in compression can be varied tuning the carbon layer characteristics (initial density and thickness) and the laser intensity, with the possibility to determine the reflectivity of carbon and the position on the phase diagram. An increase of reflectivity in carbon has been observed at 260 GPa and 14 000 K while no increase in reflectivity is found at 200 GPa and 20 000 K.

A new era of laser based plasma accelerators is emerging following the commissioning of many high power laser facilities around the world. Extremely short (tens of fs) laser pulses with energy of multi-joules level are available at these newly built facilities. Here we describe the new 220 TW FLAME facility. In particular we discuss the laser system general layout, the main measurements on the laser pulse parameters, the underground target area. Finally we give an overview of the first results of the Self-Injection Test Experiment (SITE), obtained at a low laser energy. This initial low laser energy experimental campaign was necessary for the validation of the radio-protection shielding (Esposito, 2011 [1]) we discuss here. With respect to our preliminary configuration, with a pulse duration of 30 fs and a focusing optic of F/15, we discuss here the minimum laser energy requirements for electron acceleration and the forward transmitted optical radiation. (C) 2012 Elsevier B.V. All rights reserved.

We studied the behavior of porous carbon compressed by laser-generated shock waves. In particular, we developed a new design for targets, optimized for the investigation of carbon reflectivity at hundred-GPa pressures and eV/k temperatures. Specially designed “two-layer-two materials” targets, comprising porous carbon on transparent substrates, allowed the probing of carbon reflectivity and a quite accurate determination of the position in the P, T plane. This was achieved by the simultaneous measurement of shock breakout times, sample temperature (by optical pyrometry) and uid velocity. The experiments proved the new scheme is reliable and appropriate for reflectivity measurements of thermodynamical states lying out of the standard graphite or diamond hugoniot. An increase of reflectivity in carbon has been observed at 260 GPa and 14,000 K while no increase in reflectivity is found at 200 GPa and 20,000 K. We also discuss the role of numerical simulations in the optimization of target parameters and in clarifying shock dynamics.

Many experiments, based on the road map of the European High Power laser Energy Research facility project, were performed to study fast electron transport in compressed matter in the context of fast ignition approach to inertial confinement fusion. The generation of high intensity beams from laser-matter interaction extends the possibility to use protons as a diagnostic to image imploding targets in these experiments. The analysis of experimentally obtained proton images requires a careful analysis and accurate numerical simulations using both hydrodynamic and Monte Carlo (MC) codes. An experiment has been performed in 2008 at Rutherford Appleton Laboratory to study fast electron propagation in cylindrical imploding targets illuminated by four laser pulses. In this paper, we present new simulation results in 3-D geometry. Three-dimensional density map is generated by running the 3-D version of the MULTI code. Proton radiography images are then simulated using the MC code MCNPX. © 2011 IEEE.

Fast electrons produced by a 10 ps, 160 J laser pulse through laser-compressed plastic cylinders are studied experimentally and numerically in the context of fast ignition. K(alpha)-emission images reveal a collimated or scattered electron beam depending on the initial density and the compression timing. A numerical transport model shows that implosion-driven electrical resistivity gradients induce strong magnetic fields able to guide the electrons. The good agreement with measured beam sizes provides the first experimental evidence for fast-electron magnetic collimation in laser-compressed matter.

The advance in laser-plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular, the upcoming experiments with the 250 TW laser at the FLAME facility of the INFN Laboratori Nazionali di Frascati, will enter the GeV regime with more than 100 pC of electrons. At the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need for developing a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV), with still unknown angular divergences. Within the PlasmonX experiment at FLAME, a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence, present challenges in the design and construction of such a device. We present the design considerations for this spectrometer that lead to the use of scintillating fibers, multichannel photo-multipliers and a multiplexing electronics, a combination which is innovative in the field. We also present the experimental results obtained with a high intensity electron beam performed on a prototype at the LNF beam test facility. (C) 2011 Elsevier B.V. All rights reserved.

In this paper experimental measures of the reflectivity change in carbon compressed to megabar pressures are presented. The experiments were performed at ILE, Osaka University. The GEKKO-XII laser facility was used to produce shock waves into two-layertwo-materials targets made of porous carbon deposited on a transparent substrate. Target design allowed the exploration of the phase diagram by means of samples with different carbon initial density and exploiting the reflection of the shock wave at the interface between carbon and the denser substrate to increase pressure. At the same time, carbon reflectivity could be probed with a secondary laser pulse through the transparent substrate. Also, shock dynamics has been studied thoroughly with numerical simulations performed with the hydrodynamical-radiative code Multi. An increase in carbon reflectivity was evidenced at 2.5 Mbar and 14,000 K. © 2011 Elsevier B.V.

This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to 'advanced ignition schemes', i.e. the fast ignition and the shock ignition approaches to inertial fusion. Such schemes are aimed at achieving a higher gain, as compared with the classical approach which is used in NIF, as required for future reactors, and make fusion possible with smaller facilities. In particular, a series of experiments related to fast ignition were performed at the RAL (UK) and LULI (France) Laboratories and studied the propagation of fast electrons (created by a short-pulse ultra-high-intensity beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar) laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling in the 10 16 W cm -2 intensity regime of interest for shock ignition. © 2011 IOP Publishing Ltd.

An automated autocorrelator based on a first-order auto-correlation function has been designed and assembled for measuring femtosecond pulses from lasers operating at a high-frequency repetition rate. In particular, it has been used to characterize the laser oscillator Time-Bandwidth GLX 200. The autocorrelator scheme is based on a Michelson interferometer; the linear displacement of the movable mirror, signals from the photodiode (IRPD) (autocorrelation function), pulse duration calculation and statistics were controlled and recorded by an I/O digital card and a dedicated Labview program. Our results can effectively reproduce the reference data provided by the manufacturer. The system can be successfully applied to low-energy pulses since the operating threshold energy relies on IRPD sensitivity only.

By the year 2010 a new laser will be operational at the CNR Campus in Pisa. The laser system will deliver two beams each one providing 1-ns 50-joule pulses of high optical quality and full control of phase. The major feature of the system is its spectral and time shape flexibility ranging from narrowband single mode operation to broadband operation with pulse tailoring. According to previous experiments and recent simulations, these features could critically determine the laser-pellet coupling in the different approaches to laser fusion. The physics involved in the different coupling processes is still not fully investigated experimentally. The BLISS laser, combined with the rest of the ILIL experimental facility, including ultrafast optical probing, time resolved optical X-ray diagnostics and particle detection could contribute to this investigation with ad hoc small scale experiments. The main features of the innovative BLISS laser front end for broadband operation are shown, together with the amplification chain and the main features of the experimental installation. Data from simulations providing a useful input for future experiments are also presented. BLISS is expected to contribute to the preparatory phase of the large scale European HiPER project. © 2010 American Institute of Physics.

International audience; Smoothing of laser beam non-uniformities using gas jets has been studied. The experiment has been performed with the PALS laser working at 0.44 ?m with an intensity of about 1015 W/cm2. The laser beam has been split in two by a prism thus creating an artificial large-scale non-uniformity (?90 ?m). We recorded time resolved and static images of laser-gas jet interaction with and without an Al target. Multi 1D and 2D simulations show that such interaction acts redistributing the over-intensities over larger surface. This effect has to be attributed to ionization processes with consequent laser beam refraction. Results show that Argon gas jet produces a strong refraction of the laser beam thus strongly reducing the initial two spots separation. © EDP Sciences and Springer 2009.

International audience; The process of laser beam homogenization in a gas medium placed in front of a thin metallic foil has been studied. Experiments were performed using the Prague Asterix Laser System iodine laser [ Jungwirth et al., Phys. Plasmas 8, 2495 (2001) ] working at 0.44 μm wavelength and irradiance of about 10^15 W/cm^2. Homogenization was detected both by directly analyzing the transmitted laser beam and by studying the shock breakout on the foil rear side. Results show that the gas ionization by the laser pulse induces a strong refraction and produces an effective smoothing of large-scale intensity nonuniformities.

Femtosecond laser pulse propagation in monomode optical fibers is demonstrated and investigated numerically (by simulations) and experimentally in this paper. A passively mode locked Nd:glass laser giving a pulse duration of about 200 fsec at 1053 nm wavelength and 120 mW average optical power with 100 MHz repetition rate is used in the experimental work. Numerical simulations are done by solving the nonlinear Schrödinger equation with the aid of Matlab program. The results show that self phase modulation (SPM) leads to compression of the spectral width from 5 nm to 2.1 nm after propagation of different optical powers (34, 43, 86 and 120 mW) in fibers of different length (5, 15, 35 m). The varying optical powers produced a varying phase shift. The output spectral width also changed with the fiber length at a given peak power. © 2009 World Scientific Publishing Company.

International audience; We studied the process of laser beam homogenization in a gas medium placed in front of a thin metallic foil. Experiments were performed using the Prague PALS iodine laser working at 0.44 µm wavelength and irradiances of about 10^15 W cm^−2. Homogenization was detected both by directly analysing the transmitted laser beam and by studying the shock breakout on the foil rear side. Results show that the gas ionization by the laser pulse induces a strong refraction and produces an effective smoothing of large-scale intensity non-uniformities.

We analyze the results of a recent experiment performed at the PALS laboratory and concerning ablation pressure at 0.44 µm laser wavelength measured at irradiance up to 2 × 1014 W/cm2. Using the code “ATLANT,” we have performed two-dimensional (2D) hydrodynamics simulations. Results show that 2D effects did not affect the experiment and also give evidence of the phenomenon of delocalized absorption of laser light.

International audience; We present the experimental results, and their analysis, connected to the possibility to control laser inhomogeneities exploiting the non-uniform electron density distribution created by the laser while propagating in a gas jet. The induced self-refraction in the plasma created in the gas medium results in re-distributing local over-intensities over larger surfaces. The experiment at the PALS laser facility has been performed creating a large non-uniformity by a wedge arrangement and recording the static and dynamic images with and without the coupling to an Al target.

The interaction of a picosecond Nd: YAG laser ( wavelength 532 nm, pulse duration 40 ps) with a polycrystalline titanium nitride ( TiN) film was studied. The TiN thin film was deposited by physical vapour deposition on a silicon substrate. The titanium nitride/ silicon system was modified with an energy fluence from 0.2 to 5.9 J cm(-2). Multi- pulse irradiation was performed in air by a focused laser beam. Surface modifications were analysed after 1 - 100 successive laser pulses. Depending on the laser pulse energy and pulse count, the following phenomena were observed: ( i) increased surface roughness, ( ii) titanium nitride film cracking, ( iii) silicon substrate modification, ( iv) film exfoliation and ( v) laser- induced periodical surface structures on nano- ( NPSS) and micro- dimensions ( MPSS). Photon 2006 Conference, Sep 04-07, 2006, Univ Manchester, Manchester, England

We propose the use of Focused Ion Beam/Scanning Electron Microscope (FIB/SEM) devices for the analysis of ablation results. Ablated samples have been obtained by irradiating an Al planar target with an optically smoothed iodine laser working at 0.44 μm. The interpretation of FIB images shows the high potentiality of the technique.

In this paper we describe the experimental validation of the technique of correction of wavefront aberration in the middle of the laser amplifying chain. This technique allows the correction of the aberrations from the first part of the laser system, and the pre-compensation of the aberrations built in the second part. This approach will allow an effective aberration management in the laser chain, to protect the optical surfaces and optimize performances, and is the only possible approach for multi-Petawatt laser system from the technical and economical point of view. This approach is now possible after the introduction of new deformable mirrors with lower static aberrations and higher dynamic than the standard devices.

Nitrogen lasers have been used for many years to make dye solutions lase. A nitrogen laser, which transverse electrical discharge in gas at atmospheric pressure has been built in our laboratory. It has been characterized and applied to pump different dyes: Rhodamine 6G, Coumarin 440, DOTCI, and pyranine in simple “on axis” geometric configuration. It has been shown that pyranine can lase in the absence of any optical external mirror cavity, this happens at very low threshold, and in different solvents. Dyes under consideration can be grouped into two major classes according to their lasing behavior independently on their concentration in the solvent: Rhodamine 6G and DOTCI can lase both axially or transversally and Coumarin 440 and pyranine can lase only axially. Other intriguing features have been observed that span from simultaneous multiple beam generation, to super fluorescence and to distribute axial pumping of dye solutions. A preliminary basis for understanding and controlling such processes is the spatial energy distribution and the energy density of the beam.

We present the results of some recent experiments performed at the LULI laboratory using the 100 TW laser facility concerning the study of the propagation of fast electrons in gas targets. Novel diagnostics have been implemented including chirped shadowgraphy and proton radiography. Proton radiography images did show the presence of very strong fields in the gas probably produced by charge separation. In turn, these imply a slowing down of the fast electron cloud as it penetrates in the gas, and a strong inhibition of propagation. Indeed chirped shadowgraphy images show a strong reduction of the electron cloud velocity from the initial value close to a fraction of c.

In this paper we present Hugoniot data for plastic foams obtained with laser-driven shocks. Relative equation-of-state data for foams were obtained using Al as a reference material. The diagnostics consisted in the detection of shock breakout from double layer Al/foam targets. The foams [poly(4-methyl-1-pentene) with density 130 > rho > 60 mg/cm3] were produced at the Institute of Laser Engineering of Osaka University. The experiment was performed using the Prague PALS iodine laser working at 0.44 microm wavelength and irradiances up to a few 10(14) W/cm2. Pressures as high as 3.6 Mbar (previously unreached for such low-density materials) where generated in the foams. Samples with four different values of initial density were used, in order to explore a wider region of the phase diagram. Shock acceleration when the shock crosses the Al/foam interface was also measured.

A high brightness crystal spectrograph was designed and successfully used to study the x-ray Kalpha spectrum of aluminum as a diagnostic for target heating due to suprathermal electrons in subpicosecond laser-solid interaction experiments. Conical geometry was chosen in order to enhance spatial focusing, since an extremely low signal-to-noise ratio was expected for the photon flux, and to have a reasonable spectral range while occupying only a small solid angle within the target chamber. Very high image brightness is obtained through strong spatial focusing, as well as good spectral resolution. A simple analytical model and three-dimensional numerical simulation are presented to describe the crystal characteristics. The performance of the spectrograph was tested both on an optical bench and with a ray-tracing code. The experimental spectra allowed us to estimate the target temperature and characterize the fast electron transport. The spectrograph is considered to be particularly useful, in the configuration described here, for high power laser experiments where the solid angle accessible to the spectrograph is small and blast and debris damage from the laser produced plasma is significant. (C) 2004 American Institute of Physics.

Soft X-ray Contact Microscopy (SXCM) of Caenorhabditis elegans nematodes with typical length similar to 800 mum and diameter similar to 30 mum has been performed using the PALS laser source of wavelength lambda = 1.314 mum and pulse duration tau ( FWHM) = 400 ps. Pulsed soft X-rays were generated using molybdenum and gold targets with laser intensities I greater than or equal to 10(14) W/cm(2). Images have been recorded on PMMA photo resists and analyzed using an atomic force microscope operating in contact mode. Cuticle features and several internal organs have been identified in the SXCM images including lateral field, cuticle annuli, pharynx, and hypodermal and neuronal cell nuclei.

We studied the transport of an intense electron beam produced by high intensity laser pulses through metals and insulators. Targets were irradiated at two different intensities, 1017 W/cm2 and 1019 W/cm2, at the laser facility Xtreme Light XL-III in Beijing, a Ti:Sa laser source emitting 40 fs pulses at 800 nm. The main diagnostic was Cu - K α fluorescence imaging. Images of K α spots have been collected for those two laser intensities, for different target thickness, and for different materials. Experimental results are analyzed taking into account both collisional and collective effects as well as refluxing at the edge of the target. The target temperature is evaluated to be Tc ∼ 6 eV for intensity I 1017 W/cm2 (for all the tested materials: plastic, aluminium, and copper), and Tc ∼ 60 eV in aluminium and 120 eV in titanium for intensity I 1019 W/cm2. © 2013 American Institute of Physics.

Ultra-intense laser interaction with solid targets appears to be an extremely promising technique to accelerate ions up to several MeV, producing beams that exhibit interesting properties for many foreseen applications. Nowadays, most of all the published experimental results can be theoretically explained in the framework of the target normal sheath acceleration (TNSA) mechanism proposed by Wilks [Phys. Plasmas 8(2), 542 (2001)10.1063/1.1333697]. As an alternative to numerical simulation various analytical or semi-analytical TNSA models have been published in the latest years, each of them trying to provide predictions for some of the ion beam features, given the initial laser and target parameters. However, the problem of developing a reliable model for the TNSA process is still open, which is why the purpose of this work is to enlighten the present situation of TNSA modeling and experimental results, by means of a quantitative comparison between measurements and theoretical predictions of the maximum ion energy. Moreover, in the light of such an analysis, some indications for the future development of the model proposed by Passoni and Lontano [Phys. Plasmas 13(4), 042102 (2006)10.1063/1.2184067] are then presented. © 2012 American Institute of Physics.

Fast ignition requires a precise knowledge of fast electron propagation in a dense hydrogen plasma. In this context, a dedicated HiPER (High Power laser Energy Research) experiment was performed on the VULCAN laser facility where the propagation of relativistic electron beams through cylindrically compressed plastic targets was studied. In this paper, we characterize the plasma parameters such as temperature and density during the compression of cylindrical polyimide shells filled with CH foams at three different initial densities. X-ray and proton radiography were used to measure the cylinder radius at different stages of the compression. By comparing both diagnostics results with 2D hydrodynamic simulations, we could infer densities from 2 to 11 g/cm(3) and temperatures from 30 to 120 eV at maximum compression at the center of targets. According to the initial foam density, kinetic, coupled (sometimes degenerated) plasmas were obtained. The temporal and spatial evolution of the resulting areal densities and electrical conductivities allow for testing electron transport in a wide range of configurations. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3578346]

An experimental investigation about laser beam homogenization using gas jets is presented in this paper. The results, obtained at PALS iodine laser facility using the 3 omega wavelength and irradiances of about 10(15) W/cm(2), showed that the use of high pressure gas jets (up to 10 bar of Argon) can be effective in reducing strong laser beam non-uniformities artificially introduced by inserting a wedge arrangement on half of the beam.

We present a control system, which allows an automatic optimization of the pulse train stability in a mode-locked laser cavity. In order to obtain real-time corrections, we chose a closed loop approach. The control variable is the cavity length, mechanically adjusted by gear system acting on the rear cavity mirror, and the controlled variable is the envelope modulation of the mode-locked pulse train. Such automatic control system maintains the amplitude of the mode-locking pulse train stable within a few percent rms during the working time of the laser. Full implementation of the system on an Nd:yttrium lithium fluoride actively mode-locked laser is presented.

Soft X-ray contact microscopy (SXCM), using a pulsed X-ray source, offers the possibility of imaging the ultrastructure of living biological systems at sub-100 nm resolution, We have developed a table-top pulsed plasma S-ray source for this application, generated by a large-volume XeCl laser, achieving a good conversion efficiency to 'water-window' X-rays (hv approximate to 280-530 eV). Optimum plasma conditions for SXCM are discussed, including the effect of pulse duration, target material and resist development time on image resolution. Soft X-ray contact images of Chlamydomonas dysosmos (unicellular alga) and of the cyanobacterium Leptolyngbya are shown.