I. Yu. Skobelev

Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field

Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recently discovered x-ray emission features observed in low-density regions at the base of protostellar jets, such as the well-studied jet HH 154. A scaled-down plasma experiment shows that axial magnetic fields in young stars can shape their bipolar jet outflows. Stellar outflows replicated in miniature Astronomers observe tight bright jets beaming from the poles of many celestial objects. But what focuses them so well? Albertazzi et al. recreated a scaled-down plasma jet in a laboratory setting to match the behavior of those in young stellar objects. The experiments show that the jets are collimated by a poloidal magnetic field aligned with the same axis. A conelike shock also emerges, as the expanding plasma is abruptly confined by the magnetic field. Science, this issue p. 325

High-resolution x-ray spectrometer based on spherically bent crystals for investigations of femtosecond laser plasmas

Ultrashort-pulse, laser-produced plasmas have become very interesting laboratory sources to study spectroscopically due to their very high densities and temperatures, and the high laser-induced electromagnetic fields present. Typically, these plasmas are of very small volume and very low emissivity. Thus, studying these near point source plasmas requires advanced experimental techniques. We present a new spectrometer design called the focusing spectrometer with spatial resolution (FSSR-2D) based on a spherically bent crystal which provides simultaneous high spectral (λ/Δλ≈104) and spatial resolution (≈10 μm) as well as high luminosity (high collection efficiency). We described in detail the FSSR-2D case in which a small, near point source plasma is investigated. An estimate for the spectral and spatial resolution for the spectrometer is outlined based on geometric considerations. Using the FSSR-2D instrument, experimental data measured from both a 100 fs and a nanosecond pulse laser-produced plasma are pr...

Generation of X rays and energetic ions from superintense laser irradiation of micron-sized Ar clusters

AbstractHigh-resolutionK-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters havebeen measured with an intensity above 10 19 W0cm 2 and a pulse duration of 30 fs. The total photon flux of 2310 8 photons0pulse was achieved for He a1 resonant line of Ar ~l 5 3.9491 A, 3.14 keV !. In parallel with X-raymeasurements,energydistributionsofemittedionshavebeenmeasured.Themultiplychargedionswithkineticenergiesup to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoricheating of clusters and shift the ion balance toward the higher charge states, which enhances both the X-ray line yield ofthe He-like argon ion and the ion kinetic energy.Keywords: Cluster; High power laser; Isochoric heating; Multiply charged ion; X ray 1. INTRODUCTIONRecent development of ultrashort, high peak-power lasersystems, based on the chirped pulse amplification ~CPA!technique, opens up a new regime of laser–matter inter-action ~Perry & Mourou, 1994!. Nowadays a focusing ofsuch laser pulses produces laser peak intensities well above10

Portable, tunable, high-luminosity spherical crystal spectrometer with an x-ray charge coupled device, for high-resolution x-ray spectromicroscopy of clusters heated by femtosecond laser pulses

A portable (200×100×100 mm3), high-luminosity, spherically bent crystal spectrometer was designed for measuring in a wide spectral range of 1.2–19.6 A very low emissivity x-ray spectra of different clusters heated by 35 fs laser radiation. This spectrometer is associated with a custom design x-ray charge coupled device that features a large sensitive area (24.6×24.6 mm2) and a small pixel size (24×24 μm2). This apparatus provides simultaneous high spectral (λ/δλ∼1000–5000) and spatial (40–80 μm) resolution. A large (30×10 mm2) open aperture mica crystal with R=100 mm is used as the dispersive and focusing element. The large tuneability of the spectrometer makes it possible to record high-resolution spectra of H-like ions of oxygen (CO2 clusters) in a spectral range of 15–17 A, Ne-like like ions of Kr in a spectral range of 5–5.7 A, and He-like spectra of Ar in a spectral range of 3.0–3.4 and 3.7–4.4 A without any adjustment of the spectrometer setup. Thanks to the high luminosity (high collection efficien...

Pulse duration effect on the distribution of energetic particles produced by intense femtosecond laser pulses irradiating solids

The energy distribution of hot electrons produced by a very short, intense laser pulse (I=2/4×1018 W/cm2, 60 fs, λ=800 nm, obliquely incident p polarized) is investigated theoretically via particle simulation and experimentally via measurements of the electron distribution in the MeV region and the Doppler-shifted emission spectrum of fast ions. This energy distribution is shown to be greatly different from the known two-temperature distribution. The hot electrons with energies near the maximal (∼2 MeV) constitute the distribution with an effective temperature Th considerably higher than that of lower-energy electrons, which dominate the emission of energetic ions. The temperature scaling with the laser intensity differs from the known Th∼I1/2.

Exotic dense-matter states pumped by a relativistic laser plasma in the radiation-dominated regime

In high-spectral resolution experiments with the petawatt Vulcan laser, strong x-ray radiation of KK hollow atoms (atoms without n = 1 electrons) from thin Al foils was observed at pulse intensities of 3 × 10(20) W/cm(2). The observations of spectra from these exotic states of matter are supported by detailed kinetics calculations, and are consistent with a picture in which an intense polychromatic x-ray field, formed from Thomson scattering and bremsstrahlung in the electrostatic fields at the target surface, drives the KK hollow atom production. We estimate that this x-ray field has an intensity of >5 × 10(18) W/cm(2) and is in the 3 keV range.

X-ray radiation from ions with K-shell vacancies

Abstract 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 10 19 W/cm 2 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 n e ≈3×10 23 cm −3 at temperatures between kT e =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 He α -line and the region from the He β -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.

Acceleration of highly charged GeV Fe ions from a low-Z substrate by intense femtosecond laser

Almost fully stripped Fe ions accelerated up to 0.9 GeV are demonstrated with a 200 TW femtosecond high-intensity laser irradiating a micron-thick Al foil with Fe impurity on the surface. An energetic low-emittance high-density beam of heavy ions with a large charge-to-mass ratio can be obtained, which is useful for many applications, such as a compact radio isotope source in combination with conventional technology.

X-ray spectra of fast ions generated from clusters by ultrashort laser pulses

The high precision X-ray spectroscopy studies of plasma created from the CO 2 clusters in gas jet targets by the ultrashort laser pulses (35 and 60 fs duration) were performed at the intensities I L ∼ 10 17 –10 18 W cm −2 . The spectral line shape of the H-like and He-like oxygen ions gains an asymmetry with increasing the laser pulse intensity. Theoretical modeling of the line shape shows that the asymmetry can be explained by absorption of the Doppler-shifted line radiation from the essential fraction of ions (over 10 −3 ) with energies above 1 MeV due to photoionization of inner shells of carbon ions. The results obtained demonstrate measurement capabilities of the X-ray spectral measurements of multicharged ions accelerated during the interaction with a laser radiation.

Characteristic features of the x-ray spectra of a plasma produced by heating CO2 clusters by intense femtosecond laser pulses with λ=0.8 and 0.4 μm

The x-ray spectra of a plasma produced by heating CO2 clusters with intense femtosecond laser pulses with λ=0.8 μm and λ=0.4 μm are investigated. Spatially resolved x-ray spectra of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally that such a plasma contains quite a large relative number of ions (≃10−2–10−3) with energies of 0.1–1 MeV. The contour of the OVIII Lyα line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic pulses. These features cannot be explained by any mechanisms known to the authors.