Optically controlled dense current structures driven by relativistic plasma aperture-induced diffraction

Abstract

(2016). Optically controlled dense current structures driven by relativistic plasma aperture-induced diffraction. Nature Physics, 12, 505-512. DOI: 10.1038/nphys3613 General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights.Take down policy The Research Portal is Queen's institutional repository that provides access to Queen's research output. Every effort has been made to ensure that content in the Research Portal does not infringe any person's rights, or applicable UK laws. If you discover content in the Research Portal that you believe breaches copyright or violates any law, please contact openaccess@qub.ac.uk. AbstractThe collective response of charged particles to intense fields is intrinsic to plasma accelerators and radiation sources, relativistic optics and many astrophysical phenomena. Here we show that the fundamental optical process of diffraction of intense laser light occurs via the self-generation of a relativistic plasma aperture in thin foils undergoing relativistic induced transparency. The plasma electrons collectively respond to the resulting near-field diffraction pattern, producing a beam of energetic electrons with spatial structure which can be controlled by variation of the laser pulse parameters. It is shown that static electron beam, and induced magnetic field, structures can be made to rotate at fixed or variable angular frequencies depending on the degree of ellipticity in the laser polarization. The concept is demonstrated numerically and verified experimentally. It is a viable step towards optical control of charged particle dynamics in laser-driven sources. * Electronic address: paul.mckenna@strath.ac.uk 1 The formation of current structures due to the collective response of charged particles to a perturbation is one of the most fundamental properties of plasma. This is manifest in plasma dynamics ranging from flares and X-ray jets on the sun to disruptive instabilities in fusion plasmas. This feature is also exploited to great effect in the development of compact laser-based particle accelerators and radiation sources, which have wide-ranging potential applications in science, medicine and industry. Controlling the collective motion of plasma electrons in response to perturbation produced by intense laser light is key to the development of these novel sources. Pertinent examples in plasma with density low enough for laser light to propagate (underdense plasma) include the self-generated plasma cavity or 'bubble' produced in laser-driven wakefield acceleration [1] and plasma channels [2]. These structures are formed principally by the ponderomotive force induced by the propagating laser pulse, which expels electrons from the regions of high laser intensity, and by self-generated fields induced by the current displacement [3]. Sh...

Beyond the ponderomotive limit: Direct laser acceleration of relativistic electrons in sub-critical plasmas

“…Therefore, the analysis is well suited to make meaningful predictions regarding electron acceleration in near-critical and over-critical plasmas, provided that such plasmas are relativistically transparent to the incoming high-intensity laser pulse 28,29 . However, wave propagation becomes a crucial aspect in this case and it should be addressed selfconsistently 30 taking into account transverse laser pulse dimensions and its polarization 31,32 .…”

Intra-pulse transition between ion acceleration mechanisms in intense laser-foil interactions

“…Signature features in the spatial-intensity distribution of the resultant ion beam, including the onset of transverse instabilities and differences in the directionality, show that TNSA, RPA, and transparency-enhanced processes can all occur at different phases of the interaction. [20][21][22] In this article, a characterization of the intra-pulse transition from the radiation pressure-dominated to the relativistic transparency regime in ultrathin foil targets is presented. By measuring changes to the divergence of a low-energy, annular component of the proton beam, the time within the laser pulse envelope at which relativistic induced transparency (RIT) occurs can be inferred.…”

Influence of laser polarization on collective electron dynamics in ultraintense laser–foil interactions

“…The most salient results for all three polarization cases of the collective electron motion investigation for this target undergoing significant relativistic transparency are shown in Figures 5(a-c). A more detailed analysis of these results are reported in Gonzalez-Izquierdo et al [19] . A double-lobe distribution in the electron density is measured in the case of linearly polarized light, with the axis separating the lobes orientated perpendicular to the laser polarization axis ( Figure 5(a)).…”

“…As n c and λ are intrinsic parameters of the laser, the effective parameter which determines the onset of relativistic transparency in ultrathin targets is the areal density, n e l. We have recently reported on the collective response of target electrons to intense laser light in ultrathin targets for which significant hole boring occurs, in the near-critical density regime [16][17][18][19] . Using picosecond duration laser pulses and ultrathin Al targets, Powell et al [17] demonstrated that the onset of transparency can produce a directed jet of energetic electrons in the expanding plasma.…”

“…For shorter (∼40 fs) pulses, it is shown by Gray et al [16] that in the case of targets with thickness on the threshold for transparency, the electron beam distribution becomes elliptical, with the major axis of the ellipse determined by the laser polarization direction. Focusing on thinner targets, GonzalezIzquierdo et al [19] showed that a relativistic plasma aperture produced during transparency induces diffraction of the transmitted laser light. The resulting spatial modification of the electron beam is shown to be sensitive to the degree of ellipticity of the polarization.…”