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

TL;DR

This paper investigates ionization by intense, short laser pulses, revealing the formation of broad supercontinua without interference patterns, influenced by radiation pressure, and demonstrating the potential for generating short electron pulses.

Contribution

It introduces the concept of supercontinua in ionization spectra under relativistic laser pulses and analyzes their formation and properties using numerical and saddle-point methods.

Findings

Supercontinua extend over hundreds of photon energies.

Ionization spectra lack interference patterns in supercontinua.

Electrons can form short-duration pulses within the supercontinuum.

Abstract

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.