Towards an in situ, full-power gauge of the focal-volume intensity of petawatt-class lasers

Abstract

About 50 years ago, Sarachick and Schappert [Phys. Rev. D. 1, 2738-2752(1970] showed that relativistic Thomson scattering leads to wavelength shifts that are proportional to the laser intensity. About 28 years later Chen et al. [Nature 396, 653-655 (1998)] used these shifts to estimate their laser intensity near 10 18 W/cm 2 . More recently there have been several theoretical studies aimed at exploiting nonlinear Thomson scattering as a tool for direct measurement of intensities well into the relativistic regime. We present the first quantitative study of this approach for intensities between 10 18 and 10 19 W/cm 2 . We show that the spectral shifts are in reasonable agreement with estimates of the peak intensity extracted from images of the focal area obtained at reduced power. Finally, we discuss the viability of the approach, its range of usefulness and how it might be extended to gauge intensities well in excess of 10 19 W/cm 2 .

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

“…By knowing this initial condition and measuring the frequency ω s at fixed emission angle θ one can extract the value of a 0 and, therefore, that of I = c 3 ω 2 a 2 0 /8π. This procedure was demonstrated in a recent experiment [22], where a peak value of intensity 10 18 W/cm 2 was estimated from the measurement of the second harmonic shift. NTS of laser radiation proceeded on electrons generated in the focus due to strong-field ionization of molecular nitrogen at a backing pressure 10 −3 mbar.…”

“…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.…”

“…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].…”

Reflecting petawatt lasers off relativistic plasma mirrors: a realistic path to the Schwinger limit

“…A different approach is clearly required. The accurate measurement of high laser intensities ( 10 16 W/cm 2 ) is actually still an unsolved problem, which has resisted all efforts of the ultrahigh-intensity research community for more than 25 years [98] . Yet, for initial experiments on SF QED a reasonable initial goal would be to estimate an order of magnitude of the light intensity, and to prove that large boosts are induced, not to accurately determine an intensity value.…”

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.…”