An extended model of the quantum free-electron laser

TL;DR

This paper introduces a comprehensive one-dimensional quantum free-electron laser model without averaging or boundary conditions, revealing new effects like quantum diffusion damping of spontaneous emission and electron recoil dynamics.

Contribution

It presents an extended QFEL model that captures electron diffusion and recoil effects, advancing understanding beyond previous averaged models.

Findings

Electron confinement to a 2-level system in steady-state.

First demonstration of coherent spontaneous emission in QFEL.

Quantum diffusion dampens spontaneous emission in pulsed regime.

Abstract

Previous models of the quantum regime of operation of the Free Electron Laser (QFEL) have performed an averaging and the application of periodic boundary conditions to the coupled Maxwell - Schrodinger equations over short, resonant wavelength intervals of the interaction. Here, an extended, one-dimensional model of the QFEL interaction is presented in the absence of any such averaging or application of periodic boundary conditions, the absence of the latter allowing electron diffusion processes to be modeled throughout the pulse. The model is used to investigate how both the steady-state (CW) and pulsed regimes of QFEL operation are affected. In the steady-state regime it is found that the electrons are confined to evolve as a 2-level system, similar to the previous QFEL models. In the pulsed regime Coherent Spontaneous Emission (CSE) due to the shape of the electron pulse current distribution is shown to be present in the QFEL regime for the first time. However, unlike the classical case, CSE in the QFEL is damped by the effects of quantum diffusion of the electron wavefunction. Electron recoil from the QFEL interaction can also cause a diffusive drift between the recoiled and non-recoiled parts of the electron pulse wavefunction, effectively removing the recoiled part from the primary electron-radiation interaction.