Radiation reaction enhancement in flying focus pulses

M Formanek,J P Palastro,A Di Piazza,D Ramsey

doi:10.1103/physreva.105.l020203

Abstract

Radiation reaction (RR) is the oldest still-unsolved problem in electrodynamics. In addition to conceptual difficulties in its theoretical formulation, the requirement of exceedingly large charge accelerations has thus far prevented its unambiguous experimental identification. Here, we show how measurable RR effects in a laser-electron interaction can be achieved through the use of flying focus pulses (FFPs). By allowing the focus to counterpropagate with respect to the pulse phase velocity, a FFP overcomes the intrinsic limitation of a conventional laser Gaussian pulse (GP) that limits its focus to a Rayleigh range. For an electron initially also counterpropagating with respect to the pulse phase velocity, an extended interaction length with the laser peak intensity is achieved in a FFP. As a result, the same RR deceleration factors are obtained, but at FFP laser powers orders of magnitude lower than for ultrashort GPs with the same energy. This renders the proposed setup much more stable than those using GPs and allows for more accurate \emph{in situ} diagnostics. Using the Landau-Lifshitz equation of motion, we show numerically and analytically that the capability of emerging laser systems to deliver focused FFPs will allow for a clear experimental identification of RR.

Highlights

Radiation reaction (RR), i.e., the energy and momentum loss of an accelerated charge as it emits radiation, remains an outstanding issue in the formulation of classical electrodynamics [1–3]
Recent experiments utilizing high-intensity lasers [31,32] operated in a regime where quantum effects “interfered” with classical RR, complicating their physical interpretation
Several studies have illustrated the advantage of flying focus pulses (FFPs) for a wide range of laser-based applications, including ionization waves in plasma [38,39], photon acceleration [40], laser wakefield acceleration [35], vacuum electron acceleration [41], and nonlinear Thomson scattering [42]

Summary

Introduction

Radiation reaction (RR), i.e., the energy and momentum loss of an accelerated charge as it emits radiation, remains an outstanding issue in the formulation of classical electrodynamics [1–3]. An ultrarelativistic electron traveling in the opposite direction of the phase fronts can remain in the “focus” of a FFP for extended interaction times limited only by the total pulse energy. If spatial focusing effects are ignored, i.e., for a plane wave characterized by the envelope g(φ), and if a pulse counterpropagating with respect to an ultrarelativistic electron is considered, the wave-electron interaction time tint is approximately given by τ /2.

Results

Conclusion