Supercontinuum in ionization by relativistically intense and short laser pulses: ionization without interference and its time analysis

Ionization by relativistically intense laser pulses of finite duration is considered in the framework of strong-field quantum electrodynamics. Our main focus is on the formation of ionization supercontinua. More specifically, when studying the energy distributions of photoelectrons ionized by circularly polarized pulses, we observe the appearance of broad structures lacking the interference patterns. These supercontinua extend over hundreds of driving photon energies, thus corresponding to high-order nonlinear processes. The corresponding polar-angle distributions show asymmetries which are attributed to the radiation pressure experienced by photoelectrons. Moreover, our time analysis shows that the electrons comprising the supercontinuum can form pulses of short duration. While we present the fully numerical results, their interpretation is based on the saddle-point approximation for the ionization probability amplitude.Comment: 13 pages, 10 figure

Trident pair creation by a train of laser pulses: Resonance, threshold, and carrier envelope phase effects

General formulation in the realm of strong-field quantum electrodynamics is provided for a process that occurs in the presence of a train of laser pulses and, in the tree level, is represented by a two-vertex Feynman diagram with exchange of a virtual photon. A scheme of retrieving resonances in the corresponding probability distributions is also formulated in these general settings. While the presented formalism is applicable to a variety of processes like electron-positron pair creation and annihilation, M\"oller scattering, Bhabha scattering, etc., we illustrate it for a trident process. Specifically, we consider electron-positron pair creation in the muon--laser-field collisions. We demonstrate that the probability distributions exhibit integrable singularities close to the threshold of pair creation. Also, a variety of resonances is observed that originate from the poles of the Feynman photon propagator. While those resonances are, in general, obscured by strong quantum interferences, we show that they can be isolated by changing the carrier envelope phase of the driving laser pulses. In that case, while transformed into the Lorentz-Breit-Wigner shape profile, the resonance position and width can be determined.Comment: 15 pages, 9 figure