The photonic free-electron laser: a numerical study of its fundamental physics

Photonic crystals (PhC) can radically control the propagation and emission of light [1]. This has been utilized to control the emission properties of embedded light sources, such as quantum dots [2–6]. PhC lasers have been set-up using this control to demonstrate unique lasers, showing e.g., ultrafast modulation of spontaneous emission rates and edge emitting quantum cascade lasers [7,8]. However, the wavelength of PhC lasers is still controlled by the embedded emitters as the light emission occurs due to electronic transitions between discrete energy levels of bound electrons [9]. Essentially any wavelength can be emitted by free electrons propagating through a vacuum as continuous electron levels provide the emitting transitions [9]. These so-called free-electron lasers emit coherent radiation when close synchronism between the interacting electromagnetic wave and a plasma wave on the electron beam exists [10,11]. By adjusting the initial velocity of the electron the synchronism shifts to a different wavelength.