Correlated two-photon emission by transitions of Dirac-Volkov states in intense laser fields: QED predictions

Abstract

In an intense laser field, an electron may decay by emitting a pair of photons. The two photons emitted during the process, which can be interpreted as a laser-dressed double Compton scattering, remain entangled in a quantifiable way: namely, the so-called concurrence of the photon polarizations gives a gauge-invariant measure of the correlation of the hard gamma rays. We calculate the differential rate and concurrence for a backscattering setup of the electron and photon beam, employing Volkov states and propagators for the electron lines, thus accounting nonperturbatively for the electron-laser interaction. The nonperturbative results are shown to differ significantly compared to those obtained from the usual double Compton scattering.

Approximating higher-order nonlinear QED processes with first-order building blocks

“…n γ2 → −n γ2 and n γ1;3 → n γ1;3 , and finally multiplying with an overall −1. The sign change for one of the components of n γ can be understood as a consequence of the fact that, when changing an incoming photon to an outgoing one, one takes the complex conjugate of the polarization vector ϵ μ , which in (20) corresponds to λ → −λ, which in turn changes the sign of n γ2 in (21). The goal is now to link together these first-order terms to approximate higher-order processes for sufficiently long pulses or large a 0 .…”

“…After the first photon emission the photon can decay via nonlinear Breit-Wheeler pair production [4,5] γ → e − þ e þ or the electron can emit a second photon. The first gives one part of the nonlinear trident process [6][7][8][9][10][11][12][13][14][15][16][17][18] e − → e − þ e − þ e þ , and the second gives one part of double nonlinear Compton scattering [19][20][21][22][23][24][25][26] e − → e − þ γ þ γ. Since all the processes we consider here are in general nonlinear in the interaction with the laser, we will drop "nonlinear" from here on.…”

Positron energy distribution in factorized trident process

“…Our study is devoted to an analysis of the energy spectra of positrons (e + ) produced in collisions of ultrarelativistic electrons (e − ) with a high-intensity laser beam (L, cicular polarization), e − + L → e − + e + e − , where e − is the recoil electron. This is the trident process which, analog to the nonlinear two-photon Compton process [1][2][3], is described within the Furry picture by a prototypical two-vertex diagram and its exchange part. Quantum interference effects make a throughout description quite challenging.…”

Trident process in laser pulses

“…This, however, will likely change soon, given the great deal of interest in this process in itself [14][15][16][17] and as a first step towards production of many particles in cascades [18][19][20]. A related second-order process is double nonlinear Compton scattering [21][22][23][24][25][26][27][28], where the electron instead produces two photons.…”