Characterizing extreme laser intensities by ponderomotive acceleration of protons from rarified gas

Abstract

A new method to diagnose extreme laser intensities through measurement of angular and spectral distributions of protons directly accelerated by the laser focused into a rarefied gas is proposed. We simulated a laser pulse focused by an off-axis parabolic mirror by Stratton-Chu integrals, that enables description of laser pulse with different spatial-temporal profiles focusing in a focal spot down to the diffraction limit, that makes our theoretical predictions be a basis for experimental realization. The relationship between characteristics of the proton distributions and parameters of the laser pulse have been analyzed. The analytical and numerical results obtained justify the new method of laser diagnostics. The proposed scheme should be valuable for the commissioning of new extreme intensity laser facilities.

Focal-shape effects on the efficiency of the tunnel-ionization probe for extreme laser intensities

“…The requirements of locality and low target density leave only few effects to consider as potential candidates for an in situ intensity probe. So far, tunnel ionization [18,27,29,31], nonlinear Thomson scattering [21][22][23] and ponderomotive scattering of electrons [23,24] and protons [25] were examined by virtue of reaching this objective. Below we briefly describe these effects giving a more detailed account of the method based on tunnel ionization.…”

“…This approach has been theoretically examined for electrons and protons, see e.g. recent publications [24,25,36] and references there. Scattering of charged particles on a laser focus in the limit of low density, when the self field of the beam makes no effect on the particle dynamics and radiation, have been widely considered starting from the pioneering work by Kibble [37].…”

“…Besides, additional constraints are imposed on the parameters of the electron beam introducing extra difficulties into the experimental scheme and increases uncertainties in the interpretation of results. In [25] the laser pulse diagnostics, based on the detection of momentum distributions of protons produced in ionization of a rarified hydrogen target and ponderomotively accelerated from the laser focus, was theoretically examined. In the nonrelativistic domain of intensities for protons, I ≤ 10 24 W/cm 2 the method was shown to reliably determine the peak value of intensity via the cut-off position in the energy spectra of protons.…”

“…Last time, several proposals for experimental characterization of a laser focus at extreme intensities have been discussed. The list of currently examined methods for in situ intensity measurement includes diagnostics based on multiple tunneling ionization of heavy atoms [18][19][20], on scattering of laser light by electrons [21][22][23], and on ponderomotive scattering of electrons or protons in the laser focus [23][24][25]. In this paper, we continue our analysis of the atomic diagnostics based on the observation of tunneling ionization of multi-electron atoms in a laser focus [18][19][20].…”

Pair production seeded by electrons in noble gases as a method for the laser intensity diagnostics

“…Nevertheless, the determination of the peak intensity of such strong laser pulses represents a formidable task. Recently, a number of various techniques have been extensively discussed in the literature: measuring yields of highly charged ions due to atomic ionization [11][12][13], detecting the light scattering or additional radiation due to the interaction between electrons and the laser field [14][15][16][17][18][19], or the analysis of photoionization or direct acceleration of charged particles [20][21][22][23][24][25][26][27] (see also references therein). In the present paper we discuss how the laser intensity diagnostics can be carried out using the strongfield QED mechanism of pair production due to the interaction of free electrons or free xenon atoms with an intense laser field.…”