Exotic Dense-Matter States Pumped by a Relativistic Laser Plasma in the Radiation-Dominated Regime (original) (raw)
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K-shell spectra of solid Al excited by petawatt picosecond laser pulses have been investigated at the Vulcan PW facility. Laser pulses of ultrahigh contrast with an energy of 160 J on the target allow studies of interactions between the laser field and solid state matter at 1e20 W/cm2. Intense X-ray emission of KK hollow atoms (atoms without n = 1 electrons) from thin aluminum foils is observed from optical laser plasma for the first time. Specifically for 1.5 um thin foil targets the hollow atom yield dominates the resonance line emission. It is suggested that the hollow atoms are predominantly excited by the impact of X-ray photons generated by radiation friction to fast electron currents in solid-density plasma due to Thomson scattering and bremsstrahlung in the transverse plasma fields. Numerical simulations of Al hollow atom spectra using the ATOMIC code confirm that the impact of keV photons dominates the atom ionization. Our estimates demonstrate that solid-density plasma generated by relativistic optical laser pulses provide the source of a polychromatic keV range X-ray field of 1e18 W/cm2 intensity, and allows the study of excited matter in the radiation-dominated regime. High-resolution X-ray spectroscopy of hollow atom radiation is found to be a powerful tool to study the properties of high-energy density plasma created by intense X-ray radiation.
High-Resolved X-ray Spectra of Hollow Atoms in a Femtosecond Laser-Produced Solid Plasma
Physica Scripta, 1999
A new type of quasi-continuous spectra of femtosecond laser plasma in the vicinity of multicharged H-like and He-like ion resonance lines were observed and interpreted for the ¢rst time. It is shown that such spectra were generated by multicharged hollow ions and are caused by super high density conditions provided by a high contrast laser pulse.
EPL (Europhysics Letters), 2016
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 innermost shells of light atoms. Hollow ions spectral diagnostics provide a unique opportunity to characterize powerful x-ray radiation of laboratory and astrophysical plasmas. The ability of bright photon sources to rapidly remove the inner-shell electrons from atoms has become an exciting area of research in recent years since it encompasses a region that lies on the boundary of atomic and plasma physics. This is in part due to the increasing availability of such radiation-generating sources as XFELs [1-5] and next-generation petawatt laser facilities that can generate high-intensity x-ray fields [6]. These experimenp-1
Inner-shell ionization of potassium atoms ionized by a femtosecond laser
Physical Review A, 2006
With a femtosecond laser pulse we rapidly ionize potassium atoms ͑K 0 ͒ in the gas phase, generating potassium ions ͑K + ͒, and monitor the altered energy-level scheme with a subsequent hard x-ray pulse. Removal of the potassium 4s valence electron increases the binding energies of both the valence and the 1s core levels, and induces an ultrafast change of the 1s-4p x-ray transition energy by about 2.8 eV. We simultaneously observe a 50% increase in oscillator strength of K + over K 0 for that transition.
X-ray radiation from ions with K-shell vacancies
Journal of Quantum Spectroscopy and Radiation Transfer 65, 477-499 (2000), 2000
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].
Hollow Atoms: a Theoretical Challenge
Physica Scripta, 2001
Hollow atoms are characterized by a large number of vacant inner shells and electrons occupying the outer shells. These``exotic''atomic species are formed in collision processes between highly-charged ions and several types of targets. The scope of the present contribution is to examine the decay properties of hollow atom states populated in collision with atoms, molecules, solid surfaces and clusters.
Laser-driven inner-shell excitation in high-Z atoms: a shell-selective impact ionization mechanism
Summary form only given. The efficient generation of inner-shell population inversion in high-Z elements (Z>30) is the most direct route to the development of an atom-based coherent multi-kilovolt X-ray source (i.e. a∼1 A X-ray laser). We describe a shell-selective, coherent impact ionization mechanism which is capable of providing a required pumping rate in excess of 1W/atom for the generation of inner-shell population inversion in laser-driven plasmas. The evidence for the existence of such a mechanism is contained in the Xe L-shell (2p←3d) emission spectra obtained under laser excitation of 5-20 atom Xe clusters at irradiances of 1018-1019 W/cm2. The spectra display three striking features: (i) the generation of "hollow" atoms, including the inverted ions Xe27+(2p53d10) and Xe28+(2p53d9), (ii), a∼1000× reduction in the efficiency of Xe(L) emission as the pump-laser wavelength is increased by a factor of ∼3 from 248 nm to 800 nm2 and, most significantly, (iii) the obs...
Creation and diagnosis of a solid-density plasma with an X-ray free-electron laser
Nature, 2012
Matter with a high energy density (.10 5 joules per cm 3 ) is prevalent throughout the Universe, being present in all types of stars 1 and towards the centre of the giant planets 2,3 ; it is also relevant for inertial confinement fusion 4 . Its thermodynamic and transport properties are challenging to measure, requiring the creation of sufficiently long-lived samples at homogeneous temperatures and densities 5,6 . With the advent of the Linac Coherent Light Source (LCLS) X-ray laser 7 , high-intensity radiation (.10 17 watts per cm 2 , previously the domain of optical lasers) can be produced at X-ray wavelengths. The interaction of single atoms with such intense X-rays has recently been investigated 8 . An understanding of the contrasting case of intense X-ray interaction with dense systems is important from a fundamental viewpoint and for applications. Here we report the experimental creation of a solid-density plasma at temperatures in excess of 10 6 kelvin on inertial-confinement timescales using an X-ray free-electron laser. We discuss the pertinent physics of the intense X-ray-matter interactions, and illustrate the importance of electron-ion collisions. Detailed simulations of the interaction process conducted with a radiative-collisional code show good qualitative agreement with the experimental results. We obtain insights into the evolution of the charge state distribution of the system, the electron density and temperature, and the timescales of collisional processes. Our results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological systems, material science investigations, and the study of matter in extreme conditions.