Free-Electron–Bound-Electron Resonant Interaction

Here we present a new paradigm of free-electron–bound-electron resonant interaction. This concept is based on a recent demonstration of the optical frequency modulation of the free-electron quantum electron wave function (QEW) by an ultrafast laser beam. We assert that pulses of such QEWs correlated in their modulation phase, interact resonantly with two-level systems, inducing resonant quantum transitions when the transition energy $\mathrm{\Delta }E=\hslash {\omega }_{21}$ matches a harmonic of the modulation frequency ${\omega }_{21}=n{\omega }_b$. Employing this scheme for resonant cathodoluminescence and resonant EELS combines the atomic level spatial resolution of electron microscopy with the high spectral resolution of lasers.

Figure 1

A density-modulated quantum electron wave packet (a) passing near a two-level system (2LS) target (b), and exciting transitions and luminescence. (c) Enhanced excitation by a train of modulation-phase correlated QEWs.

Figure 2

Comparison of upper level population probability buildups by the field excitation of a pulse of modulated QEWs. (a) Excitation of Rabi oscillation with correlated wave packets: Green curve, QEWs arrive at equal time spacing; blue, at random time $t_{0j}$; black, a continuous modulated QEW. (b) Same, with uncorrelated modulated QEWs (${\phi }_{0j}$ random); black is the average of events.