The way in which electrons interact with photons (the particles of light) is a vital part of many modern technologies, from LEDs to solar panels. But the interaction is inherently weak due to a major scale mismatch: the wavelength of visible light is about 1,000 times longer than an electron, so how the two affect each other is constrained by that disparity.
Now, researchers at the University of Hong Kong in China, the Massachusetts Institute of Technology (MIT) in the United States, and other institutions have devised a revolutionary way to enable more robust interactions between photons and electrons, which produces a dramatic increase in the emission of light from a phenomenon called “Smith-Purcell radiation”.
This breakthrough is sure to have major implications for fundamental scientific research and commercial applications, although it will require more years of research to put into practice.
Through a combination of computer simulations and laboratory experiments, Yi Yang’s (University of Hong Kong) team found that using an electron beam with a specially designed photonic crystal (a slab of silicon on an insulator, with nanometer-scale holes) ) it is possible to achieve many orders of magnitude more intense emission than would normally be possible in conventional Smith-Purcell radiation. In the tests carried out, these researchers have recorded radiation about 100 times greater.
Artist’s impression of the interaction between free electrons and flat bands in a photonic crystal slab. (Image: Lei Chen)
Unlike other methods for producing light sources or other electromagnetic radiation, the method based on free electrons is fully tunable: it can produce emissions of any desired wavelength, simply by adjusting the size of the photonic structure and the speed of the electrons. This can make it especially valuable for making emission sources at wavelengths that are difficult to produce efficiently, such as terahertz waves, ultraviolet light, and X-rays.
Yang and his colleagues report the technical details of their discovery and tests in the academic journal Nature, under the title “Photonic flatband resonances for free-electron radiation.” (Fountain: NCYT by Amazings)