Proposed Studies Of Radiation Damping In Laser Interaction With An Ultra-thin, Coherently Reflecting Electron Sheet, Regarded As A Macro-particle

Abstract

We introduce the concept of an ultra‐thin, dense electron sheet as a macro‐particle—similar to an electron microbunch of an FEL—where N electrons coherently reflect in the inner rest frame of the bunch. This ultra‐thin electron sheet is pushed out off an ultra‐thin Diamond‐Like Carbon (DLC) target by a driver laser and acts as a relativistic flying mirror [1, 2] for a production laser. The space charge forces of the electron sheet are balanced by the trapping fields of the driver laser, of the remaining ion sheet and of the counter propagating production laser, resulting in longitudinally bound electrons. Like in the Mössbauer effect of nuclei the photon recoil is taken up by the N electrons of the macro‐particle. The Landau‐Lifshitz equation [3] for the classical radiation damping reaction of an external laser force Fext, here especially the Lorentz force, has been deduced as the first and second term in a Taylor series expansion ∑n = o∞(1/n!)(τ0)ndnFext/dtn, where τ0 = 2e2/(3 mec3) = r0/c is the critical time and r0 is the classical electron radius. For the macro‐particle the mass me is replaced by M = N⋅me, the charge e by q = N⋅e and the critical time τ0 by τmac = N⋅τ0. Thus the reflected fields and the radiation damping fields can be strongly enhanced and studied experimentally. Here we can test experimentally how higher order terms of the Taylor expansion contribute. For higher orders n the number N is reduced due the reduced coherence volume of the electron sheet, resulting in a convergence of the power series. Possible higher order terms increase the reflectivity of the relativistic mirror further and lead to much higher fields, which may even reach the Schwinger limit for the vacuum. They also would result in Doppler boosted higher order Landau‐Lifshitz harmonics. In quantum mechanics new acceleration radiation effects like the Unruh effect [4, 5] are predicted, where now the single detector‐like electron may be replaced by the N electron macro‐particle, again enhancing the Unruh radiation strongly. In this way a coherently reflecting macro‐particle will lead to a new world of high field physics and will allow to verify the right extensions of radiation damping.