Study of forward accelerated fast electrons in ultrashort Ti K α sources

X-ray conversion of ultra-short laser pulses on a solid sample: Role of electron waves excited in the pre-plasma

“…ps pulse, like in the experiment of Ref. 13. Moreover, they found that the strong dependence of the Ka emission on the angle of the incidence and polarization of laser light was consistent with hot electrons generated by resonance absorption.…”

“…Moreover, we note that the increase of X-ray emission measured in the incidence plane (by the CCD) when polarization changes from S to P-approximately a factor 1.6-is much less than the increase, approximately by a factor 5, measured outside the angle of incidence (by the PIN-X), when the polarization rotates from P to S. These observations provide evidence of anisotropy in the X-ray conversion (in the spectral range we have detected), a clear proof of the strong contribution of electron plasma waves generated by instabilities to the laser energy conversion into X-rays. Previous works already found, separately, a dependence on the laser light polarization of either Ka emission 13,14 or parametric instabilities. 16,17 Such a separation was due to the fact that Ka generation was studied in conditions where the ultrafast laser interaction with the critical density was dominant, while parametric instabilities were considered independently from X-ray conversion efficiency.…”

“…10 In some cases, these studies were aimed at characterizing X-ray sources 11 and study hot electron generation. 12,13 However, little information on the role of polarization emerged from these studies, due to the long pre-plasma, which prevented significant interaction at the critical density. Moreover, with ultra-short pulses, the pre-plasma scale length and the conditions for the growing of the instabilities are very different.…”

A novel single-shot, spectrally resolved x-ray imaging technique of ICF relevant plasmas

“…18 In this field, the main diagnostics is the Kα emission spectroscopy, eventually from ad hoc fluorescent tracer layers, which is routinely performed by using bent (spherical or toroidal) Bragg crystals coupled either to X-ray film (or image plates) or to Charge Coupled Device (CCD) cameras. [19][20][21][22][23] While allowing a very high spectral resolution to be obtained, bent Bragg crystals suffer from a low diffraction efficiency. 24 Furthermore, heating by return current may result in a loss of the effective efficiency of the crystal at the selected wavelength as well as in artifacts in the reconstructed 2D image of the X-ray emitting source.…”

Intra-cycle depolarization of ultraintense laser pulses focused by off-axis parabolic mirrors

“…For instance, laser-plasma interaction processes depending on the laser polarization, such as, among others, the ones involved in proton acceleration, via either target normal sheath acceleration or radiation pressure acceleration (see Refs. [4,5] and references therein), or the excitation of parametric instabilities [6][7][8] , are normally modelled using focused pulses with an ideal space and time structure. The detailed study of the structure of the electromagnetic field of beams focused by means of parabolic surfaces was initially undertaken in the field of optical microscopy, and thus devoted to the investigation of on-axis reflecting parabolic surfaces.…”