190 research outputs found
High resolution X-ray emission spectra from picosecond laser irradiated Ge targets
Investigations of a high resolution X-ray emission spectrum in the range 0.66–0.75 nm obtained by irradiating a Germanium target with high-power p-polarized, 40 picosecond laser radiation at 532 nm wavelength was done. Spectra in the wavelength region of 2l-4l′ and 2l-5l′ L-shell transitions in F-like, Ne-like and Na-like germanium ions were recorded using the FSSR-2D spectrometer equipped with a spherically bent quartz crystal with a spectral resolution λ/Δλ better than 5000. Spectral lines were compared with theoretical values obtained using the LANL plasma kinetic code ATOMIC. Fair agreement between experimental and theoretical spectral lines has been observed, which allowed to measure enough high bulk electron temperature values of 560 eV and electron density of ∼1021 cm−3 in Ge plasma irradiated by rather small commercial high repetition rate Nd:YAG laser system
Shadow monochromatic backlighting: Large-field high resolution X-ray shadowgraphy with improved spectral tunability
The shadow monochromatic backlighting (SMB) scheme, a modification
of the well-known soft X-ray monochromatic backlighting scheme,
is proposed. It is based on a spherical crystal as the dispersive
element and extends the traditional scheme by allowing one to
work with a wide range of Bragg angles and thus in a wide spectral
range. The advantages of the new scheme are demonstrated
experimentally and supported numerically by ray-tracing
simulations. In the experiments, the X-ray backlighter source
is a laser-produced plasma, created by the interaction of an
ultrashort pulse, Ti:Sapphire laser (120 fs, 3–5 mJ,
1016 W/cm2 on target) or a short wavelength
XeCl laser (10 ns, 1–2 J, 1013 W/cm2 on
target) with various solid targets (Dy, Ni + Cr, BaF2).
In both experiments, the X-ray sources are well localized spatially
(∼20 μm) and are spectrally tunable in a relatively wide
wavelength range (λ = 8–15 Å). High quality monochromatic
(δλ/λ ∼ 10−5–10−3)
images with high spatial resolution (up to ∼4 μm) over a large field
of view (a few square millimeters) were obtained. Utilization
of spherically bent crystals to obtain high-resolution, large
field, monochromatic images in a wide range of Bragg angles
(35° < Θ < 90°) is demonstrated for the first
time
Lithium fluoride coloration by laser-plasma soft x-rays: A promising tool for X-ray microscopy and photonics
A new imaging detector for EUV or soft-X-ray radiation based on optically stimulated luminescence (OSL) of lithium fluoride (LiF) films or crystals is presented. The first micro-radiography images of biological samples and of meshes obtained on LiF using a laser-plasma source or an X-ray laser are shown, and (up to now) a resolution better than one micron is demonstrated. The dependence of the coloration density vs the deposited X-ray dose is considered and the advantages of this new diagnostic technique for both coherent and non-coherent EUV sources, compared with CCDs detectors, photographic films and photoresists are discussed. This new detector is extremely suitable for laser plasmas and for X-ray lasers sources
Effect of plastic coating on the density of plasma formed in Si foil targets irradiated by ultra-high-contrast relativistic laser pulses
The formation of high energy density matter occurs in inertial confinement fusion, astrophysical, and geophysical systems. In this context, it is important to couple as much energy as possible into a target while maintaining high density. A recent experimental campaign, using buried layer (or "sandwich" type) targets and the ultrahigh laser contrast Vulcan petawatt laser facility, resulted in 500 Mbar pressures in solid density plasmas (which corresponds to about 4.6×107J/cm3 energy density). The densities and temperatures of the generated plasma were measured based on the analysis of X-ray spectral line profiles and relative intensities
Using X-ray spectroscopy of relativistic laser plasma interaction to reveal parametric decay instabilities : A modeling tool for astrophysics
By analyzing profiles of experimental x-ray spectral lines of Si XIV and Al XIII, we found that both Langmuir and ion acoustic waves developed in plasmas produced via irradiation of thin Si foils by relativistic laser pulses (intensities ∼1021 W/cm2). We prove that these waves are due to the parametric decay instability (PDI). This is the first time that the PDI-induced ion acoustic turbulence was discovered by the x-ray spectroscopy in laser-produced plasmas. These conclusions are also supported by PIC simulations. Our results can be used for laboratory modeling of physical processes in astrophysical objects and a better understanding of intense laser-plasma interactions
Evidence of high-n hollow ion emission from Si ions pumped by ultraintense x-rays from relativistic laser plasma
We report on the first observation of high-n hollow ions (ions having no electrons in the K or L shells) produced in Si targets via pumping by ultra-intense x-ray radiation produced in intense laser-plasma interactions reaching the radiation dominant kinetics regime. The existence of these new types of hollow ions in high energy density plasma has been found via observation of highly-resolved x-ray emission spectra of silicon plasma, and confirmed by plasma kinetics calculations, underscoring the ability of powerful radiation sources to fully strip electrons from the inner-most shells of light atoms. Hollow ions spectral diagnostics provide a unique opportunity to characterize powerful x-ray radiation of laboratory and astrophysical plasmas
ACCURATE WAVELENGTH MEASUREMENTS AND MODELING OF Fe XV TO Fe XIX SPECTRA RECORDED IN HIGH-DENSITY PLASMAS BETWEEN 13.5 AND 17 A
Iron spectra have been recorded from plasmas created at three different laser plasma facilities: the Tor Vergata University laser in Rome (Italy), the Hercules laser at ENEA in Frascati (Italy), and the Compact Multipulse Terawatt (COMET) laser at LLNL in California (USA). The measurements provide a means of identifying dielectronic satellite lines from Fe XVI and Fe XV in the vicinity of the strong 2p → 3d transitions of Fe XVII. About 80 Δn ≥ 1 lines of Fe XV (Mg-like) to Fe XIX (O-like) were recorded between 13.8 and 17.1 A with a high spectral resolution (λ/Δλ ≈ 4000); about 30 of these lines are from Fe XVI and Fe XV. The laser-produced plasmas had electron temperatures between 100 and 500 eV and electron densities between 1020 and 1022 cm-3. The Hebrew University Lawrence Livermore Atomic Code (HULLAC) was used to calculate the atomic structure and atomic rates for Fe XV-XIX. HULLAC was used to calculate synthetic line intensities at Te = 200 eV and ne = 1021 cm-3 for three different conditions to illustrate the role of opacity: optically thin plasmas with no excitation-autoionization/dielectronic recombination (EA/DR) contributions to the line intensities, optically thin plasmas that included EA/DR contributions to the line intensities, and optically thick plasmas (optical depth ≈200 μm) that included EA/DR contributions to the line intensities. The optically thick simulation best reproduced the recorded spectrum from the Hercules laser. However, some discrepancies between the modeling and the recorded spectra remain
Soft X-ray harmonic comb from relativistic electron spikes
We demonstrate a new high-order harmonic generation mechanism reaching the
`water window' spectral region in experiments with multi-terawatt femtosecond
lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving
uJ/sr pulses. Harmonics are collectively emitted by an oscillating electron
spike formed at the joint of the boundaries of a cavity and bow wave created by
a relativistically self-focusing laser in underdense plasma. The spike
sharpness and stability are explained by catastrophe theory. The mechanism is
corroborated by particle-in-cell simulations
High-order alloharmonics produced by nonperiodic drivers
High-order harmonics are ubiquitous in nature and present in electromagnetic,
acoustic, and gravitational waves. They are generated by periodic nonlinear
processes or periodic high-frequency pulses. However, this periodicity is often
inexact, such as that in chirped (frequency-swept) optical waveforms or
interactions with nonstationary matter -- for instance, reflection from
accelerating mirrors. Spectra observed in such cases contain complicated sets
of harmonic-like fringes. We encountered such fringes in our experiment on
coherent extreme ultraviolet generation via BISER, and could not interpret them
using currently available knowledge. Here, we present a comprehensive theory
based on interference of harmonics with different orders fully explaining the
formation of these fringes, which we call alloharmonics. Like atomic spectra,
the complex alloharmonic spectra depend on several integer numbers and bear a
unique imprint of the emission process, which the theory can decipher, avoiding
confusion or misinterpretation. We also demonstrate the alloharmonics in
simulations of gravitational waves emitted by binary black hole mergers.
Further, we predict the presence of alloharmonics in the radio spectra of
pulsars and in optical frequency combs, and propose their use for measurement
of extremely small accelerations necessary for testing gravity theories. The
alloharmonics phenomenon generalizes classical harmonics and is critical in
research fields such as laser mode locking, frequency comb generation,
attosecond pulse generation, pulsar studies, and future gravitational wave
spectroscopy.Comment: 29 pages, 9 figures, 3 table
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