A study of laser plasmas as X-ray sources in the 1-10 keV spectral region

An experimental investigation on X-ray emission from laser-produced plasmas is presented and the properties of such an emission of interest for application purposes are examined. Plasmas were generated by focusing 1 μm, 3 ns Nd laser pulses onto Al and Cu targets at an intensity of 1013 W/cm2. The temporal evolution of the emission and its spectral features were investigated by using an X-ray streak-camera and an X-ray photodiode. In the case of Cu targets, the analysis of the emission showed two spectral components. The main component was centered at ≈ 1.2 keV and a minor component, whose intensity was measured to be 10-3 of the previous component, was observed at ≈7 keV. The X-ray conversion efficiency, in the investigated spectral region, was measured to be 1% for Cu targets and 0.3% for Al targets

Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments

Seismology of stars is strongly developing. To address this question we have formed an international collaboration OPAC to perform specific experimental measurements, compare opacity calculations and improve the opacity calculations in the stellar codes [1]. We consider the following opacity codes: SCO, CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large differences for Fe and Ni in equivalent conditions of envelopes of type II supernova precursors, temperatures between 15 and 40 eV and densities of a few mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar results and differ from OP ones for the lower temperatures and for spectral interval values [3]. In this work we discuss the role of Configuration Interaction (CI) and the influence of the number of used configurations. We present and include in the opacity code comparisons new HULLAC-v9 calculations [5, 6] that include full CI. To illustrate the importance of this effect we compare different CI approximations (modes) available in HULLAC-v9 [7]. These results are compared to previous predictions and to experimental data. Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences 201

Measurement of XUV-absorption spectra of ZnS radiatively heated foils

Time-resolved absorption of zinc sulfide (ZnS) and aluminum in the XUV-range has been measured. Thin foils in conditions close to local thermodynamic equilibrium were heated by radiation from laser-irradiated gold spherical cavities. Analysis of the aluminum foil radiative hydrodynamic expansion, based on the detailed atomic calculations of its absorption spectra, showed that the cavity emitted flux that heated the absorption foils corresponds to a radiation temperature in the range 55 60 eV. Comparison of the ZnS absorption spectra with calculations based on a superconfiguration approach identified the presence of species Zn6+ - Zn8+ and S5+ - S6+. Based on the validation of the radiative source simulations, experimental spectra were then compared to calculations performed by post-processing the radiative hydrodynamic simulations of ZnS. Satisfying agreement is found when temperature gradients are accounted for

Radiative properties of stellar plasmas and open challenges

The lifetime of solar-like stars, the envelope structure of more massive stars, and stellar acoustic frequencies largely depend on the radiative properties of the stellar plasma. Up to now, these complex quantities have been estimated only theoretically. The development of the powerful tools of helio- and astero- seismology has made it possible to gain insights on the interiors of stars. Consequently, increased emphasis is now placed on knowledge of the monochromatic opacity coefficients. Here we review how these radiative properties play a role, and where they are most important. We then concentrate specifically on the envelopes of $\beta$ Cephei variable stars. We discuss the dispersion of eight different theoretical estimates of the monochromatic opacity spectrum and the challenges we need to face to check these calculations experimentally.Comment: 6 pages, 5 figures, in press (conference HEDLA 2010

A study of random phased laser spots

Far-field images produced using different random phase plates on a pulsed laser beam focused with various f/numbers were recorded by a charge-coupled device (CCD) camera and then analyzed. Envelope spot sizes agree with diffraction theory while mean sizes of the pattern structures have been found to be larger than the diffraction limit. The probability density distribution of intensity in the focal plane is not the expected exponential. A central symmetry of the pattern has also been seen after suitably aperturing the beam, Some consequences for the use of powerful RPP-treated laser beams in laser-plasma interactions are discussed

EFFECTS OF RANDOM-PHASE PLATES ON ABERRATED LASER-BEAMS

Far-field images produced using random phase plates on a pulsed laser beam have been recorded by a CCD and then analysed. Spot sizes agree with diffraction theory while mean sizes of the pattern structures has been found larger than diffraction limit. Probability density distribution of intensity in the focal plane has not, in most cases, the expected exponential behaviour. Images obtained with reduced beam diameter show a definite central symmetry. Preliminary measurements of the optical breakdown threshold intensity in air show that threshold can be determined with much higher accuracy with RPP smoothed beams

A STUDY OF LASER PLASMAS AS X-RAY SOURCES IN THE 1-10 KEV SPECTRAL REGION RID B-1900-2009

X-ray emission from plasmas produced by focusing the beam of a Nd laser on massive Al or Cu targets was studied. The temporal evolution of the emission was investigated by using an X-ray streak-camera. The spectral analysis of the emission was performed with both low and high resolution. The X-ray conversion efficiency, in the investigated spectral region, was measured to be 1% for Cu and slightly lower for Al. Two main spectral components were observed in the emission. In the case of Cu target, the first component was found to be centred at approximate to 1.2 keV and the second, whose intensity was measured to be 10(-3) of the previous component, at approximate to 7 keV. From line intensity ratios, obtained from high resolution spectra, we could estimate temperature and density of the emitting region

FRONT-FACE AND REAR-FACE X-RAY-EMISSION FROM LASER-IRRADIATED AL FOILS

We studied the K-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

A study of random phased laser spots

Far-field images produced using different random phase plates on a pulsed laser beam focused with various f/numbers were recorded by a charge-coupled device (CCD) camera and then analyzed. Envelope spot sizes agree with diffraction theory while mean sizes of the pattern structures have been found to be larger than the diffraction limit. The probability density distribution of intensity in the focal plane is not the expected exponential. A central symmetry of the pattern has also been seen after suitably aperturing the beam, Some consequences for the use of powerful RPP-treated laser beams in laser-plasma interactions are discussed