Characteristics of electron beams produced by the laser wakefield acceleration are presented. The dependence of the electron beam parameters on the laser focal spot size is investigated. The experimental result shows the generation of quasimonoenergetic electron beam although the laser spot size was several times larger than the plasma wavelength. Stable electron beam generation at large laser spots was owing to the stable laser propagation in plasma channels. At a small laser spot, the beam quality is poor and this is attributed to the the filamentation instability of the laser beam.

Dependence of the electron beam parameters on the stability of laser propagation in a laser wakefield accelerator

A technique of laser peen forming on a microscale has been developed, which does not require a confining (tamping) layer. This paper reports on the results of studies carried out on 75-μm-thick steel samples using pulsed Nd:YAG lasers operating at 1,064-, 532- and 355-nm wavelengths and relatively low beam powers of 5, 2.5 and 1.8 W, respectively. Empirical data are presented to demonstrate the active forming mechanism and to characterise the process. The process was found to produce a bending towards the laser beam at any angle of incidence, including at 0° (or parallel) to the surface. A bend angle of up to approximately 28° was possible when the incident angle is 90°. The process was found to be reversible by reverse side irradiation. The results from these experiments have been compared to samples formed using continuous wave thermal laser forming. The laser peen-formed samples do not show evidence of a heat-affected zone seen in thermal laser forming, which, together with thermocouple analysis, indicates that the active laser peen forming process is non-thermal.

http://chriscarey.co.uk/wp-content/uploads/2011/11/Edwards-2009-Laser-peen-forming-without-tamping-layer.pdf

Laser micro peen forming without a tamping layer

The dynamics and energy spectra of electrons driven by a relativistically intense laser pulse are analyzed. The description is based on the numerical solution of the relativistic Newton’s equation with the Lorentz force generated by a strong focused optical field. After the interaction with it, electrons retain a considerable fraction of the energy of their oscillations during the interaction. The electron postinteraction energy spectrum is calculated. The energies in the spectrum high-energy tail are determined by the laser pulse intensity at the focal spot. An approach to estimating absolute values of the laser pulse intensity based on the measurement of the energy spectra of the electrons is proposed.

Electrodynamics of electron in a superintense laser field: New principles of diagnostics of relativistic laser intensity

Results are presented from theoretical analysis and 2D PIC simulations of electron acceleration in a breaking wake plasma wave generated by a short intense laser pulse during its interaction with a finite-length underdense plasma layer. The high energy electron energy spectrum and transverse emittance are obtained. It is shown that, for laser pulse lengths above the plasma wake wavelength, the wakefield-accelerated electrons are further accelerated by the electromagnetic wave.

Electron bunch acceleration in the wake wave breaking regime

Effects of density gradient on the self-injection of plasma electrons in the phase of laser pulse wake for further acceleration, is studied for moderate laser intensities, a0⩽3. It is shown that transverse wave breaking can shorten the length of accelerated electrons, whereas effective longitudinal wave breaking requiring steep plasma density interface increases their total charge. For the considered range of laser intensities, the total charge of electrons injected by wave breaking rises exponentially with a0.

Effects of density gradient on short-bunch injection by wave breaking in the laser wake field acceleration

An improvement of laser-focused peak intensity has been achieved in a JAERI 100 TW Ti:sapphire chirped-pulse amplifier chain with a feedback controlled adaptive optics system at a 10 Hz repetition rate. Independent measurements of optical parameters of the laser pulse and an experimental tunneling ionization ratio of He atom with laser energy scaling have practically confirmed an ultrarelativistic intensity of over 1020 W · cm−2.

Characterization of a 1020 W · cm−2 Peak Intensity by Focusing Wavefront-corrected 100-TW, 10-Hz Laser Pulses

Adaptive optics was installed in JAERI 100TW laser chain. Over 102QW/cm2 peak intensity was generated at the laser focus, which was confirmed experimentally by tunneling ionization ratio of rare gas atom.

Generation and evaluation of 10/sup 20/W/cm/sup 2/ ultra-intense optical-field by focusing JAERI 100-TW, 10-Hz laser pulses

Adaptive optics is installed and demonstrated in JAERI 100 TW laser system to achieve over 10/sup 20/ W/cm/sup 2/ peak intensity at the focal spot.

Wavefront correction of a 100 TW high-peak-power, ultrashort laser pulse

We study experimentally the interaction of the shortest at present $(23\text{\ensuremath{-}}\mathrm{fs})$, relativistically intense $(20\text{\ensuremath{-}}\mathrm{TW})$, tightly focused laser pulses with underdense plasma. MeV electrons constitute a two-temperature distribution due to different plasma wave-breaking processes at a plasma density of ${10}^{20}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. These two groups of electrons are shown numerically to constitute bunches with very distinctive time durations.

Electron acceleration by a nonlinear wakefield generated by ultrashort ( 23 − fs ) high-peak-power laser pulses in plasma

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Characterization of a 1020 W · cm−2 Peak Intensity by Focusing Wavefront-corrected 100-TW, 10-Hz Laser Pulses

Generation and evaluation of 10/sup 20/W/cm/sup 2/ ultra-intense optical-field by focusing JAERI 100-TW, 10-Hz laser pulses

Wavefront correction of a 100 TW high-peak-power, ultrashort laser pulse

Electron acceleration by a nonlinear wakefield generated by ultrashort ( 23 − fs ) high-peak-power laser pulses in plasma