L. A. Gizzi

Electric field detection in laser-plasma interaction experiments via the proton imaging technique

Due to their particular properties, the beams of the multi-MeV protons generated during the interaction of ultraintense (I>1019 W/cm2) short pulses with thin solid targets are most suited for use as a particle probe in laser-plasma experiments. The recently developed proton imaging technique employs the beams in a point-projection imaging scheme as a diagnostic tool for the detection of electric fields in laser-plasma interaction experiments. In recent investigations carried out at the Rutherford Appleton Laboratory (RAL, UK), a wide range of laser-plasma interaction conditions of relevance for inertial confinement fusion (ICF)/fast ignition has been explored. Among the results obtained will be discussed: the electric field distribution in laser-produced long-scale plasmas of ICF interest; the measurement of highly transient electric fields related to the generation and dynamics of hot electron currents following ultra-intense laser irradiation of targets; the observation in underdense plasmas, after the ...

Proton imaging: a diagnostic for inertial confinement fusion/fast ignitor studies

Proton imaging is a recently proposed technique for diagnosis of dense plasmas, which favourably exploits the properties of protons produced by high-intensity laser-matter interaction. The technique allows the distribution of electric fields in plasmas and around laser-irradiated targets to be explored for the first time with high temporal and spatial resolution. This leads to the possibility of investigating as yet unexplored physical issues. In particular we will present measurements of transient electric fields in laser-plasmas and around laser-irradiated targets under various interaction conditions. Complex electric field structures have been observed in long-scale laser-produced plasmas, while global target charge-up and growth of electromagnetic instabilities have been detected following ultraintense interactions with solid targets.

X-ray emission from laser-produced plasmas

ConclusionsThe interaction of intense laser light with matter is now widely recognised as the most versatile and promising way of generating intense pulsed X-ray radiation. The scale of presently available laser systems required to set up a powerful X-ray source in a small-size laboratory, has made it possible to conceive and develop a wide range of multidisciplinary applications. Further, the fast development of powerful lasers towards higher efficiency and compact designs is giving a strong impulse to the implementation of LPP X-ray sources in advanced industrial applications. On the other hand, an intense activity is being devoted to this field by many laboratories world-wide within internationally coordinated programmes. These joint initiatives are continuously producing important scientific results. Hard X-ray emission and high-order harmonics from fs interactions are only examples of recent achievements of laser-matter interaction studies which represent a breakthrough in the field of X-ray generation.

Generation of neutral and high-density electron-positron pair plasmas in the laboratory

Electron–positron pair plasmas represent a unique state of matter, whereby there exists an intrinsic and complete symmetry between negatively charged (matter) and positively charged (antimatter) particles. These plasmas play a fundamental role in the dynamics of ultra-massive astrophysical objects and are believed to be associated with the emission of ultra-bright gamma-ray bursts. Despite extensive theoretical modelling, our knowledge of this state of matter is still speculative, owing to the extreme difficulty in recreating neutral matter–antimatter plasmas in the laboratory. Here we show that, by using a compact laser-driven setup, ion-free electron–positron plasmas with unique characteristics can be produced. Their charge neutrality (same amount of matter and antimatter), high-density and small divergence finally open up the possibility of studying electron–positron plasmas in controlled laboratory experiments.

Analyzing laser plasma interferograms with a continuous wavelet transform ridge extraction technique: the method.

Laser plasma interferograms are currently analyzed by extraction of the phase-shift map with fast Fourier transform (FFT) techniques [Appl. Opt. 18, 3101 (1985)]. This methodology works well when interferograms are only marginally affected by noise and reduction of fringe visibility, but it can fail to produce accurate phase-shift maps when low-quality images are dealt with. We present a novel procedure for a phase-shift map computation that makes extensive use of the ridge extraction in the continuous wavelet transform (CWT) framework. The CWT tool is flexible because of the wide adaptability of the analyzing basis, and it can be accurate because of the intrinsic noise reduction in the ridge extraction. A comparative analysis of the accuracy performances of the new tool and the FFT-based one shows that the CWT-based tool produces phase maps considerably less noisy and that it can better resolve local inhomogeneties.

Proton imaging detection of transient electromagnetic fields in laser-plasma interactions (invited)

Due to their particular properties (small source size, low divergence, short duration, large number density), the beams of multi-MeV protons generated during the interaction of ultraintense (I>1019 W/cm2) short pulses with thin solid targets are most suited for use as a particle probe in laser–plasma experiments. In particular, the proton beams are a valuable diagnostic tool for the detection of electromagnetic fields. The recently developed proton imaging technique employs the beams, in a point-projection imaging scheme, as an easily synchronizable diagnostic tool in laser–plasma interactions, fields, with high temporal and spatial resolution. The broad energy spectrum of the beams coupled with an appropriate choice of detector (multiple layers of dosimetric film) allows temporal multiframe capability. By allowing, for the first time, diagnostic access to electric-field distributions in dense plasmas, this novel diagnostic opens up to investigation a whole new range of unexplored phenomena. Results obtai...

Measurement of highly transient electrical charging following high-intensity laser–solid interaction

The multi-million-electron-volt proton beams accelerated during high-intensity laser–solid interactions have been used as a particle probe to investigate the electric charging of microscopic targets laser-irradiated at intensity ∼1019 W cm2. The charge-up, detected via the proton deflection with high temporal and spatial resolution, is due to the escape of energetic electrons generated during the interaction. The analysis of the data is supported by three-dimensional tracing of the proton trajectories.

Evidence of resonant surface-wave excitation in the relativistic regime through measurements of proton acceleration from grating targets.

The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, is experimentally investigated. Ultrahigh contrast (~10(12)) pulses allow us to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultrahigh intensity >10(19) W/cm(2). A maximum increase by a factor of 2.5 of the cutoff energy of protons produced by target normal sheath acceleration is observed with respect to plane targets, around the incidence angle expected for the resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance.

Impulsive electric fields driven by high-intensity laser matter interactions

Theinteractionofhigh-intensitylaserpulseswithmatterreleasesinstantaneouslyultra-largecurrentsofhighlyenergetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation andMeVionfrontexpansionattherearoflaser-irradiatedthinmetallicfoils.Laser-drivenimpulsivefieldsatthesurface of solid targets can be applied for energy-selective ion beam focusing.

Production of ultracollimated bunches of multi-MeV electrons by 35 fs laser pulses propagating in exploding-foil plasmas

Very collimated bunches of high energy electrons have been produced by focusing super-intense femtosecond laser pulses in submillimeter under-dense plasmas. The density of the plasma, preformed with the laser exploding-foil technique, was mapped using Nomarski interferometry. The electron beam was fully characterized: up to 10^9 electrons per shot were accelerated, most of which in a beam of aperture below 10^−3 sterad, with energies up to 40 MeV. These measurements, which are well modeled by three-dimensional numerical simulations, validate a reliable method to generate ultrashort and ultracollimated electron bunches.