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Intense few-cycle laser pulses have a breadth of applications in high energy density science, including particle acceleration and x-ray generation. Multi-amplifier laser system pulses have durations of tens of femtoseconds or longer. To achieve high intensities at the single-cycle limit, a robust and efficient post-compression scheme is required. We demonstrate a staged compression technique using self-phase modulation in thin dielectric media, in which few-cycle pulses can be produced. The few-cycle pulse is then used to generate extreme ultravoilet light via high harmonic generation at strong field intensities and to generate MeV electron beams via laser solid interactions at relativistic intensities.

Thin-film compression (TFC) and the focusability of high-power laser pulses after self-phase modulation in thin films at transport intensities (∼1 TW∕cm 2 ) for petawatt laser systems is demonstrated. High-energy (∼296 mJ) laser pulses are compressed from ∼55 fs to ∼31 fs. Additionally, the focusability of high-power (∼45–55 TW) flat-top laser pulses after spectral broadening in thin films is found to be largely maintained, showing only modest decreases in the energy contained in the central part of the focal spot. In light of these findings, TFC offers a method for moving toward single-cycle pulse durations at significantly higher energies than those found at present, and if beam instabilities can be mitigated, maybe even higher intensities.

Superponderomotive-energy electrons are observed experimentally from the interaction of an intense laser pulse with a relativistically transparent target. For a relativistically transparent target, kinetic modeling shows that the generation of energetic electrons is dominated by energy transfer within the main, classically overdense, plasma volume. The laser pulse produces a narrowing, funnel-like channel inside the plasma volume that generates a field structure responsible for the electron heating. The field structure combines a slowly evolving azimuthal magnetic field, generated by a strong laser-driven longitudinal electron current, and, unexpectedly, a strong propagating longitudinal electric field, generated by reflections off the walls of the funnel-like channel. The magnetic field assists electron heating by the transverse electric field of the laser pulse through deflections, whereas the longitudinal electric field directly accelerates the electrons in the forward direction. The longitudinal electric field produced by reflections is 30 times stronger than that in the incoming laser beam and the resulting direct laser acceleration contributes roughly one third of the energy transferred by the transverse electric field of the laser pulse to electrons of the super-ponderomotive tail.

High harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, to date the shortest subfemtosecond (attosecond, 10-18 s) pulses have been produced only in the extreme UV region of the spectrum below 100 eV, which limits the range of materials and molecular systems that can be explored. Here we experimentally demonstrate a remarkable convergence of physics: when midinfrared lasers are used to drive high harmonic generation, the conditions for optimal bright, soft X-ray generation naturally coincide with the generation of isolated attosecond pulses. The temporal window over which phase matching occurs shrinks rapidly with increasing driving laser wavelength, to the extent that bright isolated attosecond pulses are the norm for 2-μm driving lasers. Harnessing this realization, we experimentally demonstrate the generation of isolated soft X-ray attosecond pulses at photon energies up to 180 eV for the first time, to our knowledge, with a transform limit of 35 attoseconds (as), and a predicted linear chirp of 300 as. Most surprisingly, advanced theory shows that in contrast with as pulse generation in the extreme UV, long-duration, 10-cycle, driving laser pulses are required to generate isolated soft X-ray bursts efficiently, to mitigate group velocity walk-off between the laser and the X-ray fields that otherwise limit the conversion efficiency. Our work demonstrates a clear and straightforward approach for robustly generating bright isolated attosecond pulses of electromagnetic radiation throughout the soft X-ray region of the spectrum.

Each successive generation of x-ray machines has opened up new frontiers inscience, such as the first radiographs and the determination of the structureof DNA. State-of-the-art x-ray sources can now produce coherent high brightnesskeV x-rays and promise a new revolution in imaging complex systems on nanometreand femtosecond scales. Despite the demand, only a few dedicated synchrotronfacilities exist worldwide, partially due the size and cost of conventional(accelerator) technology. Here we demonstrate the use of a recently developedcompact laser-plasma accelerator to produce a well-collimated,spatially-coherent, intrinsically ultrafast source of hard x-rays. This methodreduces the size of the synchrotron source from the tens of metres tocentimetre scale, accelerating and wiggling a high electron chargesimultaneously. This leads to a narrow-energy spread electron beam and x-raysource that is >1000 times brighter than previously reported plasma wiggler andthus has the potential to facilitate a myriad of uses across the whole spectrumof light-source applications.

Absolute photoionization cross-section measurements for a mixture of ground and metastable states of Xe4+, Xe5+, and Xe6+ are reported in the photon energy range of 4d-nf transitions, which occur within or adjacent to the 13.5 nm window for extreme ultraviolet lithography light source development. The reported values allow the quantification of opacity effects in xenon plasmas due to these 4d-4f autoionizing states. The oscillator strengths for the 4d-4f and 4d-5f transitions in Xeq+ (q=1-6) ions are calculated using nonrelativistic Hartree-Fock and random phase approximations. These are compared with published experimental values for Xe+ to Xe3+ and with the values obtained from the present experimental cross-section measurements for Xe4+ to Xe6+. The calculations assisted in the determination of the metastable content in the ion beams for Xe5+T and Xe6+. The experiments were performed by merging a synchrotron photon beam generated by an undulator beamline of the Advanced Light Source with an ion beam produced by an electron cyclotron resonance ion source.

The production of X-rays from electron transitions into K-shell vacancies ([K.sub.α,β]) emission) is a well-known process in atomic physics and has been extensively studied as a plasma diagnostic in low- and mid-Z materials. However, X-ray spectra from near neutral high-Z ions are very complex, and their interpretation requires the use of state-of-the-art atomic calculations. In this experiment, the Titan laser system at Lawrence Livermore National Laboratory was used to deliver an approximately 350 J laser pulse, with a 10 ps duration and a wavelength of 1054 nm, to a gold (Au) target. A transparent bent quartz crystal spectrometer with a hard X-ray energy window, ranging from 17 to 102 keV, was used to measure the emission spectrum. [K.sub.α1,α2] and [K.sub.β1,γ1] transitions were observed over a range of target sizes. Additionally, a series of shots were conducted with a pre-ionizing long pulse (3 ns, 1-10 J, 527 nm) on the backside of the target. FLYCHK, an atomic non-LTE code, designed to provide ionization and population distributions, was used to model the experiment. [K.sub.α] / [K.sub.β] ratios were found to be in good agreement with the predicted value for room temperature Au targets. PACS No: 52.38.Ph La production de rayons-X provenant de transitions electroniques dans les lacunes de la couche K (emission [K.sub.α,β]) est un mecanisme bien connu en physique atomique qui a ete tres etudie comme diagnostique de plasma dans les materiaux de Z bas et intermediate. Cependant, les spectres X d'ions de Z eleve presque neutres sont tres complexes et leur interpretation exige l'utilisation de calculs atomiques de pointe. Dans cette experience, nous utilisons le systeme laser Titan du Lawrence Livermore National Laboratory qui envoie environ 350 J par impulsion d'une duree de 10 ps et une longueur d'onde de 1054 nm sur une cible d'or (Au). Nous avons utilise un spectrometre a cristal de quartz courbe avec une fenetre d'entree de rayons-X allant de 17 a 102 keV, afin de mesurer le spectre d'emission. Nous avons observe les transitions [K.sub.α1,α2] et [K.sub.β1,γ1] sur un domaine de grandeur de cible. De plus, une serie d'impulsion pre-ionisante (3 ns, 1-20 J, 527 nm) a ete tiree sur la partie arriere de la cible. Nous avons utilise le code atomique sans equilibre thermodynamique local FLYCHK pour obtenir les distributions d' ionisation et de population, afin de modeliser les resultats experimentaux. Les rapports [K.sub.α] / [K.sub.β] obtenus sont en bon accord avec les valeurs predites pour des cibles d'Au a la temperature de la piece. [Traduit par la Redaction], 1. Introduction The absorption of laser energy during high-intensity shortpulse laser-plasma interactions results in the production of a large current of hot electrons, which can subsequently generate energetic protons, ions, [...]

Electric fields induce motion in many fluid systems, including polymer melts', surfactant micelles (2) and colloidal suspensions3. Likewise, electric fields can be used to move liquid drops (4). Electrically induced droplet motion manifests itself in processes as diverse as storm cloud formation (5), commercial ink-jet printing (6), petroleum and vegetable oil dehydration', electrospray ionization for use in mass spectrometry (8), electrowetting (9) and lab-on-a-chip manipulations (10). An important issue in practical applications is the tendency for adjacent drops to coalesce, and oppositely charged drops have long been assumed to experience an attractive force that favours their coalescence (11-13). Here we report the existence of a critical field strength above which oppositely charged drops do not coalesce. We observe that appropriately positioned and oppositely charged drops migrate towards one another in an applied electric field; but whereas the drops coalesce as expected at low field strengths, they are repelled from one another after contact at higher field strengths. Qualitatively, the drops appear to 'bounce' off one another. We directly image the transient formation of a meniscus bridge between the bouncing drops, and propose that this temporary bridge is unstable with respect to capillary pressure when it forms in an electric field exceeding a critical strength. The observation of oppositely charged drops bouncing rather than coalescing in strong electric fields should affect our understanding of any process involving charged liquid drops, including de-emulsification, electrospray ionization and atmospheric conduction., The non-coalescence behaviour is readily demonstrated experimentally (Fig. 1, left), using a container with the bottom half filled with water and the top half with an immiscible and poorly conducting [...]