Nonperturbative signatures of nonlinear Compton scattering

摘要

The probabilities of various elementary laser-photon-electron/positron interactions display in selected phase space and parameter regions typical nonperturbative dependencies such as ∝ P exp { ? a E crit / E } , where P is a preexponential factor, E crit denotes the critical Sauter-Schwinger field strength, and E characterizes the (laser) field strength. While the Schwinger process with a = a S ≡ π and the nonlinear Breit-Wheeler process in the tunneling regime with a = a n ? BW ≡ 4 m / 3 ω ′ (with ω ′ the probe photon energy and m the electron/positron mass) are famous results, we point out here that also the nonlinear Compton scattering exhibits a similar behavior when focusing on high harmonics. Using a suitable cutoff c > 0 , the factor a becomes a = a n ? C ≡ 2 3 c m / ( p 0 + p 0 2 ? m 2 ) . This opens the avenue toward a new signature of the boiling point of the vacuum even for field strengths E below E crit by employing a high electron beam-energy p 0 to counter balance the large ratio E crit / E by a small factor a to achieve E / a → E crit . In the weak-field regime, the cutoff facilitates a threshold leading to multiphoton signatures showing up in the total cross section at subthreshold energies.