Effects of plastic coating on K-alpha yield from ultra-short pulse

A study of the K-alpha radiation emitted from Ti foils irradiated with intense, similar to0.2 J, 67 fs, 800 nm laser pulses, scanning a range of intensities (similar to10(15)-10(18) W cm(-2)), is reported. The brightness of single-shot K-alpha line emission from the front of the targets is recorded. The yield from bare titanium (Ti) is compared to that from plastic (parylene-E) coated Ti. It is demonstrated that, for a defocused beam, a thin layer of plastic increases the yield.

Electron and laser interactions with positive ions

Recent progress in laboratory-based electron-ion scattering is reviewed, and the sensitivity of observed interference structure as a probe of collision dynamics is discussed. The extension of our use of positive ions as scattering targets to photon-ion interactions is demonstrated with the first ion-beam measurements for the fragmentation of a molecular ion, H-2(+), using intense femtosecond laser pulses.

Short pulse laser interaction with positive ions

The viability of using beams of molecular ions as a target for strong field fragmentation studies using intense ultra-short laser pulses is demonstrated. In this way the production mechanism for multiply charged ions in strong fields may be elucidated.

Plasma Jets Driven by Ultraintense-Laser Interaction with Thin Foils

Experimental evidence of plasma jets ejected from the rear side of thin solid targets irradiated by ultraintense (> 10(19) W cm(-2)) laser pulses is presented. The jets, detected by transverse interferometric measurements with high spatial and temporal resolutions, show collimated expansion lasting for several hundreds of picoseconds and have substantially steep density gradients at their periphery. The role played by radiation pressure of the laser in the jet formation process is highlighted analytically and by extensive two-dimensional particle-in-cell simulations.

Proton Probing Measurement of Electric and Magnetic Fields Generated by ns and ps Laser-Matter Interactions

The use of laser-accelerated protons as a particle probe for the detection of electric fields in plasmas has led in recent years to a wealth of novel information regarding the ultrafast plasma dynamics following high intensity laser-matter interactions. The high spatial quality and short duration of these beams have been essential to this purpose. We will discuss some of the most recent results obtained with this diagnostic at the Rutherford Appleton Laboratory (UK) and at LULI - Ecole Polytechnique (France), also applied to conditions of interest to conventional Inertial Confinement Fusion. In particular, the technique has been used to measure electric fields responsible for proton acceleration from solid targets irradiated with ps pulses, magnetic fields formed by ns pulse irradiation of solid targets, and electric fields associated with the ponderomotive channelling of ps laser pulses in under-dense plasmas.

Laser-Driven Proton Beams: Acceleration Mechanism, Beam Optimization, and Radiographic Applications

This paper reviews recent experimental activity in the area of optimization, control, and application of laser accelerated proton beams, carried out at the Rutherford Appleton Laboratory and the Laboratoire pour l’Utilisation des Lasers Intenses 100 TW facility in France. In particular, experiments have investigated the role of the scale length at the rear of the plasma in reducing target-normal-sheath-acceleration acceleration efficiency. Results match with recent theoretical predictions and provide information in view of the feasibility of proton fast-ignition applications. Experiments aiming to control the divergence of the proton beams have investigated the use of a laser-triggered microlens, which employs laser-driven transient electric fields in cylindrical geometry, enabling to focus the emitted
protons and select monochromatic beam lets out of the broad spectrum beam. This approach could be advantageous in view
of a variety of applications. The use of laser-driven protons as a particle probe for transient field detection has been developed and
applied to a number of experimental conditions. Recent work in this area has focused on the detection of large-scale self-generated magnetic fields in laser-produced plasmas and the investigation of fields associated to the propagation of relativistic electron both on the surface and in the bulk of targets irradiated by high-power laser pulses.

Dynamic resonances and tunnelling in the multiphoton ionization of argon

We present results of wavepacket simulations for multiphoton ionization in argon. A single active electron model is applied to estimate the single-electron ionization rates and photoelectron energy distributions for lambda = 390 nm light with intensities up to I = 2 x 10(14) W cm(-2). The multiphoton ionization rates are compared with R-matrix Floquet calculations and found to be in very good agreement. The photoelectron energy distribution is used to study the nature of ionization at the higher intensities. Our results are consistent with recent calculations and experiments which show the imprint of the tunnelling process in the multiphoton regime. For few-cycle intense pulses, we find that the strong modulation of intensity and increased bandwidth leads to dynamic mixing of the 3d and 5s resonances.

A review of X-ray laser development at Rutherford Appleton Laboratory

Recent experiments undertaken at the Rutherford Appleton Laboratory to produce X-ray lasing over the 5-30 nm wavelength range are reviewed. The efficiency of lasing is optimized when the main pumping pulse interacts with a preformed plasma. Experiments using double 75-ps pulses and picosecond pulses superimposed on 300-ps background pulses are described. The use of travelling wave pumping with the approximately picosecond pulse experiments is necessary as the gain duration becomes comparable to the time for the X-ray laser pulse to propagate along the target length. Results from a model taking account of laser saturation and deviations from the speed of light c of the travelling wave and X-ray laser group velocity are presented. We show that X-ray laser pulses as short as 2-3 ps can be produced with optical pumping pulses of approximate to1-ps.

Photodissociation of D-3(+) in an intense, femtosecond laser field

H-3(+) is the simplest triatomic molecule and plays an important role in laboratory and astrophysical plasmas. It is very stable both in terms of its electronic and nuclear degrees of freedom but is difficult to study in depth in the laboratory due to its ionic nature. In this communication, experimental results are presented for the strong field dissociation of the isotopic analogue D-3(+), using 30 fs, 800 nm laser pulses with intensities up to 10(16) W cm(-2). By employing a novel experimental set-up, ions were confined in an electrostatic ion trap so that dissociation of the molecule could be studied as it radiatively cools. It was determined that dissociation could only be observed for molecules in ro-vibrational states relatively close to the dissociation limit, while more tightly bound states demonstrated remarkable stability in even the strongest fields.

Ionography of Submicron Foils and Nanostructures Using Ion Flow Generated in FS-Laser Cluster Plasma

A novel type of submicron ion radiography designed to image low-contrast objects, including nanofoils, membranes and biological structures, is proposed. It is based on femtosecond-laser-driven-cluster- plasma source of multicharged ions and polymer dosimeter film CR-39. The intense isotropic ion flow was produced by femtosecond Ti:Sa laser pulses with intensity similar to 4x10(17) W/cm(2) absorbed in the supersonic jet of the mixed He and CO2 gases. Two Focusing Spectrometers with Spatial Resolution (FSSR) were used to measure X-ray spectra of H-and He-like multicharged oxygen ions. The spectra testify that ions with energy more than 300 keV were radiated in different directions from the plasma source. High contrast ion radiography images were obtained for 2000 dpi metal mesh, 1 mu m polypropylene and 100 nm Zr foils as well as for the different biological objects. Images were recorded on a 1 mm thick CR-39 detector, placed in contact with back surface of the imaged samples at the distances 140 -160 mm from the ion source. The spatial resolution of the image no worse than 600 nm was provided. A difference in object thickness of 100 nm was very well resolved for both Zr and polymer foils. The ion radiography images recorded at different angles from the source, demonstrated almost uniform spatial distribution of ion with total number of 10(8) per shot. (C) 2009 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim

Double-ionization dynamics of laser-driven helium

We report a new method which allows sequential and non-sequential double-ionization rates in laser-driven helium to be distinguished and calculated separately. The method is applied to calculate such rates for two laser pulses, one of 0.236 au frequency and 8.0 × 1015 W cm-2 peak intensity, the other of 1.0 au frequency and also of 8.0 × 1015 W cm-2 peak intensity.

Multi-pulse scheme for enhancing electron localization through vibrational wavepacket manipulation

A novel scheme for enhancing electron localization in intense-field dissociation is outlined. Through manipulation of a bound vibrational wavepacket in the exemplar deuterium molecular ion, simulations demonstrate that the application of multiple phase-locked, few-cycle IR pulses can provide a powerful scheme for directing the molecular dissociation pathway. By tuning the time delay and carrier–envelope–phase for a sequence of pulse interactions, the probability of the electron being localized to a chosen nucleus can be enhanced to above 80%.

Laser pulse compression and amplification via Raman backscattering in plasma

A simple theoretical model is proposed for the interaction between two counter-propagating laser pulses (a pump and a seed pulse) in unmagnetized plasma. Pulse compression and amplification are observed via numerical simulation. A one dimensional fluid model for stimulated Raman backscattering is proposed to investigate the pulse compression and pulse amplification mechanisms. To accomplish this, energy is transferred from the long pump pulse to a seed pulse, with a Langmuir plasma wave mediating the transfer. The study focuses on the intensity profile of the pump laser pulse. A Gaussian and a ring intensity profile are, separately, considered for the pump laser pulse.

Evolution of elastic x-ray scattering in laser-shocked warm dense lithium

We have studied the dynamics of warm dense Li with near-elastic x-ray scattering. Li foils were heated and compressed using shock waves driven by 4-ns-long laser pulses. Separate 1-ns-long laser pulses were used to generate a bright source of 2.96 keV Cl Ly-alpha photons for x-ray scattering, and the spectrum of scattered photons was recorded at a scattering angle of 120 degrees using a highly oriented pyrolytic graphite crystal operated in the von Hamos geometry. A variable delay between the heater and backlighter laser beams measured the scattering time evolution. Comparison with radiation-hydrodynamics simulations shows that the plasma is highly coupled during the first several nanoseconds, then relaxes to a moderate coupling state at later times. Near-elastic scattering amplitudes have been successfully simulated using the screened one-component plasma model. Our main finding is that the near-elastic scattering amplitudes are quite sensitive to the mean ionization state Z and by extension to the choice of ionization model in the radiation-hydrodynamics simulations used to predict plasma properties within the shocked Li.

Time-resolved studies of ultrafast wavepacket dynamics in hydrogen molecules

Recent advances in the study of quantum vibrations and rotations in the fundamental hydrogen molecules are reported. Using the deuterium molecules (D-2(+) and D-2) as exemplars, the application of ultrafast femtosecond pump-probe experiments to study the creation and time-resolved imaging of coherent nuclear wavepackets is discussed. The ability to study the motion of these fundamental molecules in the time-domain is a notable milestone, made possible through the advent of ultrashort intense laser pulses with durations on sub-vibrational (and sub-rotational) timescales. Quantum wavepacket revivals are characterised for both vibrational and rotational degrees of freedom and quantum models are used to provide a detailed discussion of the underlying ultrafast physical dynamics for the specialist and non-specialist alike. (C) 2009 Elsevier B.V. All rights reserved.