Spontaneous and Stimulated Radiative emission of Modulated Free-Electron Quantum wavepackets - Semiclassical Analysis

TL;DR

This paper provides a semiclassical analysis of how electron quantum wavepackets emit and absorb radiation, revealing size-dependent quantum effects and potential applications in measuring wavepacket dimensions and light-matter interactions.

Contribution

It introduces a novel semiclassical framework for understanding radiative emission from modulated electron wavepackets, bridging classical and quantum regimes.

Findings

Emission depends on wavepacket size relative to wavelength.

Long wavepackets show quantum suppression of radiation.

Modulated wavepackets emit at harmonic frequencies beyond classical limits.

Abstract

Here we present a semiclassical analysis of spontaneous and stimulated radiative emission from unmodulated and optically-modulated electron quantum wavepackets. We show that the radiative emission/absorption and corresponding deceleration/acceleration of the wavepackets depend on the controllable 'history-dependent' wavepacket size. The characteristics of the radiative interaction when a wavepacket of size (duration) is short relative to the radiation wavelength, are close to the predictions of the classical point-particle modeling. On the other hand, in the long-sized wavepacket limit, the interaction is quantum-mechanical, and it diminishes exponentially at high frequency. We exemplify these effects through the scheme of Smith-Purcell radiation, and demonstrate that if the wavepacket is optically-modulated and periodically-bunched, it exhibits finite radiative emission at harmonics of the modulation frequency beyond the limit of high-frequency cutoff. Besides, the radiation analysis is further extended to the cases of superradiant emission from a beam of phase-correlated modulated electron wavepackets. This wavepacket-dependent emission process shows the radiative features of classical-to-quantum transition, indicates a way for measuring the quantum electron wavepacket size and suggests a new direction for exploring light-matter interaction.