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.

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An approach for accelerating ions, with the use of a cluster-gas target and an ultrashort pulse laser of 150-mJ energy and 40-fs duration, is presented. Ions with energy 10-20 MeV per nucleon having a small divergence (full angle) of 3.4 degrees are generated in the forward direction, corresponding to approximately tenfold increase in the ion energies compared to previous experiments using solid targets. It is inferred from a particle-in-cell simulation that the high energy ions are generated at the rear side of the target due to the formation of a strong dipole vortex structure in subcritical density plasmas.

The use of lithium fluoride ͑LiF͒ crystals and films as imaging detectors for EUV and soft-x-ray radiation is discussed. The EUV or soft-x-ray radiation can generate stable color centers, emitting in the visible spectral range an intense fluorescence from the exposed areas. The high dynamic response of the material to the received dose and the atomic scale of the color centers make this detector extremely interesting for imaging at a spatial resolution which can be much smaller than the light wavelength. Experimental results of contact microscopy imaging of test meshes demonstrate a resolution of the order of 400 nm. This high spatial resolution has been obtained in a wide field of view, up to several mm 2 . Images obtained on different biological samples, as well as an investigation of a soft x-ray laser beam are presented. The behavior of the generated color centers density as a function of the deposited x-ray dose and the advantages of this new diagnostic technique for both coherent and noncoherent EUV sources, compared with CCDs detectors, photographic films, and photoresists are discussed.

The properties of high energy density plasma are under increasing scrutiny in recent years due to their importance to our understanding of stellar interiors, the cores of giant planets 1 , and the properties of hot plasma in inertial confinement fusion devices 2 . When matter is heated by X-rays, electrons in the inner shells are ionized before the valence electrons. Ionization from the inside out creates atoms or ions with empty internal electron shells, which are known as hollow atoms (or ions) 3,4,5 . Recent advances in free-electron laser (FEL) technology 6,7,8,9 have made possible the creation of condensed matter consisting predominantly of hollow atoms. In this Letter, we demonstrate that such exotic states of matter, which are very far from equilibrium, can also be formed by more conventional optical laser technology when the laser intensity approaches the radiation dominant regime 10 . Such photon-dominated systems are relevant to studies of photoionized plasmas found in active galactic nuclei and X-ray binaries 11 . Our results promote laser-produced plasma as a unique ultra-bright x-ray source for future studies of matter in extreme conditions as well as for radiography of biological systems and for material science studies 12,13,14,15 .

Articles you may be interested inDetermination of hydrogen cluster velocities and comparison with numerical calculations J. Chem. Phys. 139, 234312 (2013); 10.1063/1.4848720 Laser initiated reactions in N2O clusters studied by time-sliced ion velocity imaging technique J. Chem. Phys. 139, 044307 (2013); 10.1063/1.4816008Coulomb explosion of ammonia clusters induced by intense nanosecond laser at 532 and 1064 nm : Wavelength dependence of the multicharged nitrogen ions A novel mathematical model for the investigations of a cluster formation process in a gas jet is presented, which enables us to obtain the detailed description of the spatial and temporal distributions of all cluster target parameters. In this model, a cluster target is considered as a two-phase medium, consisting of the continuous gas phase and the discrete condensed phase ͑clusters͒. The detailed nozzle geometry is also taken into account in this model. In order to confirm the advantage of the present model over a conventional model, a considerable amount of numerical computations has been carried out and the results are compared with the data obtained from Hagena's theory ͓Rev. Sci. Instrum. 63, 2374 ͑1992͔͒. Based on the developed modeling, a three-staged nozzle, which cannot be modeled using the conventional model, is designed for the purpose of producing a sufficient amount of micron-sized clusters. The generation of unprecedented amount of keV x rays from the laser-cluster interaction experiments with this nozzle and their accurate intensity dependences on various experimental parameters support the adequateness of the nozzle design.

X-ray spectroscopy with high spectral (up to AA/A = lo-*) and spatial resolution (up to 1 pm) is discussed. Devices based on crystals, diffraction and Bragg-Fresnel elements and their applications in Zand X-pinches and laser plasma experiments are described.

We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multiterawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving μJ/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.