Enhanced Subthresholde+e−Production in Short Laser Pulses

Abstract

The emission of e + e − pairs off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g. laser) wave field is analyzed. A significant increase of the total cross section of pair production in the subthreshold region is found for decreasing laser pulse duration even in case of moderate laser pulse intensities.PACS numbers: 12.20.Ds, 14.70.Bh The history of the study of e + e − production in γ ′ γ interaction starts with the pioneering work by Breit and Wheeler [1] published in 1934. About thirty years later, Reiss [2] and Narozhnyi, Nikishov and Ritus [3,4] have analyzed the e + e − emission off a photon γ ′ propagating in the field of an intensive polarized monochromatic electromagnetic (e.m.) plane. The e + e − production probabilities were found using the non-perturbative Volkov solutions for the electron and positron wave functions [5].If one identifies the external e.m. field with a laser pulse then most of the early work considers long lasting pulses where the temporal shape can be neglected. We denote this approach as the infinite pulse approximation (IPA). In IPA, electrons e − and positrons e + become quasi-particles with effective quasi-momenta and effective (dressed) masses. Differential and total probabilities of the e + e − pair emission depend on the reduced strength of the e.m. field, where M e is the electron mass (we use c = = 1, e 2 /4π = α = 1/137). Furthermore, the dimensionless variable ζ = s thr s is introduced, where s is the square of the total energy in the center of mass system (c.m.s.) of the Breit-Wheeler process γ ′ + γ → e + + e − and s thr = 4M 2 e is its threshold value. The Ritus variable is then defined by κ = 2ξ/ζ [4]. The case of ζ > 1 corresponds essentially to multi-photon processes. Within IPA, the minimum number of photons γ in the reaction γ ′ +nγ → e + +e − is defined as n min = I(ζ)+1, where I(ζ) is the integer part of ζ. First evidence of the multi-photon Breit-Wheeler process with ζ = 3.83 and 0.1 < ξ < 0.35 was detected at SLAC in the E-144 experiment [6], where the application of IPA is justified since the used laser pulses contain around 10 3 cycles in a shot.The rapidly evolving laser technology [7] can provide the laser power up to 10 24 -10 25 W/cm 2 in near future which is sufficient for the formation of positrons from cascade processes in the photon-electron-positron plasma [8-10] generated by photon-laser [11][12][13], electron-laser [14,15] or laser-laser interactions [16,17] (see [18] for surveys). The next generation of optical laser beams are expected to be essentially short (femtosecond duration) with only a few oscillation of the e.m. field in the pulse to be expected at ELI [19] and CLF [20] facilities. This requires the generalization of the IPA multi-photon process γ ′ + nγ → e + + e − to a finite pulse duration. Formally, this generalization may be done in a straightforward manner by substituting the expansion in Fourier series into Fourier integrals with taking into account the Volkov solution for the finite wave fie...

Charged particle dynamics in multiple colliding electromagnetic waves. Survey of random walk, Lévy flights, limit circles, attractors and structurally determinate patterns

“…see Bulanov et al (2015) and literature cited therein). These effects manifest themselves through multi-photon Compton and Breit-Wheeler effects (Nikishov & Ritus 1964a,b;Ritus 1985) (see Narozhnyi & Fofanov (1996), Boca & Florescu (2009), Ehlotzky, Krajewska & Kamiśki (2009), Heinzl, Ilderton & Marklund (2010a), Heinzl, Seipt & Kämpfer (2010b, Mackenroth & Di Piazza (2011), Krajewska & Kamiński (2012), Titov et al (2012), Harvey, Heinzl & Ilderton (2009) for recent studies), i.e. through either photon emission by an electron or positron, or electron-positron pair production by a high energy photon, respectively.…”

Vacuum refractive indices and helicity flip in strong-field QED

“…where P (pair) is the total probability of stimulated pair production by a photon of polarisation [37][38][39][40][41][42], written here using the expression (34), not previously found in the literature, in which the final state momentum integrals have been performed. The small b 0 expansion of Im T (∞) vanishes, because pair production is nonperturbative in the kinematic invariant b 0 .…”

“…The first is monochromatic; set Λ = ∞ in (42), and the others are pulsed, with Λ = 10π and Λ = π, the latter being a very short pulse. (We remark that carrier phase effects may become particularly important in short pulses, although we do not analyse this here.…”

“…where the quasimomenta obey q 2 = m 2 * , the effective mass is m [34,48,49], see (42), and nk µ represents discrete energies taken from the background. …”

“…There is for example a greater probability that the photon will 'decay' via e.g. stimulated pair production [37][38][39][40][41][42], and it follows from unitarity that 'photon persistence' probabilities must drop. As we will see below, this is associated to the appearance, at high-energy, of effects such as anomalous dispersion, which are not captured by the low-energy approximation.…”