Strengthening electron-triggered light emission


The way in which electrons interact with photons of sunshine is a key a part of many modern technologies, from lasers to solar panels to LEDs. However the interaction is inherently a weak one due to a significant mismatch in scale: A wavelength of visible light is about 1,000 times larger than an electron, so the way in which the 2 things affect one another is restricted by that disparity.

Now, researchers at MIT and elsewhere have provide you with an progressive method to make much stronger interactions between photons and electrons possible, in the method producing a hundredfold increase within the emission of sunshine from a phenomenon called Smith-Purcell radiation. The finding has potential implications for each industrial applications and fundamental scientific research, although it’ll require more years of research to make it practical.

The findings are reported today within the journal , in a paper by MIT postdocs Yi Yang (now an assistant professor on the University of Hong Kong) and Charles Roques-Carmes, MIT professors Marin Soljačić and John Joannopoulos, and five others at MIT, Harvard University, and Technion-Israel Institute of Technology.

In a mix of computer simulations and laboratory experiments, the team found that using a beam of electrons together with a specially designed photonic crystal — a slab of silicon on an insulator, etched with an array of nanometer-scale holes — they might theoretically predict stronger emission by many orders of magnitude than would ordinarily be possible in conventional Smith-Purcell radiation. Additionally they experimentally recorded a one hundredfold increase in radiation of their proof-of-concept measurements.

Unlike other approaches to producing sources of sunshine or other electromagnetic radiation, the free-electron-based method is fully tunable — it could produce emissions of any desired wavelength, just by adjusting the scale of the photonic structure and the speed of the electrons. This may occasionally make it especially useful for making sources of emission at wavelengths which can be difficult to supply efficiently, including terahertz waves, ultraviolet light, and X-rays.

The team has to this point demonstrated the hundredfold enhancement in emission using a repurposed electron microscope to operate as an electron beam source. But they are saying that the essential principle involved could potentially enable far greater enhancements using devices specifically adapted for this function.

The approach is predicated on an idea called flatbands, which have been widely explored lately for condensed matter physics and photonics but have never been applied to affecting the essential interaction of photons and free electrons. The underlying principle involves the transfer of momentum from the electron to a bunch of photons, or vice versa. Whereas conventional light-electron interactions depend on producing light at a single angle, the photonic crystal is tuned in such a way that it enables the production of an entire range of angles.

The identical process is also utilized in the wrong way, using resonant light waves to propel electrons, increasing their velocity in a way that would potentially be harnessed to construct miniaturized particle accelerators on a chip. These might ultimately give you the option to perform some functions that currently require giant underground tunnels, equivalent to the 30-kilometer-wide Large Hadron Collider in Switzerland.

“In case you could actually construct electron accelerators on a chip,” Soljačić says, “you might make rather more compact accelerators for a number of the applications of interest, which might still produce very energetic electrons. That obviously could be huge. For a lot of applications, you wouldn’t should construct these huge facilities.”

The brand new system could also potentially provide a highly controllable X-ray beam for radiotherapy purposes, Roques-Carmes says.

And the system may very well be used to generate multiple entangled photons, a quantum effect that may very well be useful within the creation of quantum-based computational and communications systems, the researchers say. “You should use electrons to couple many photons together, which is a considerably hard problem if using a purely optical approach,” says Yang. “That’s one of the vital exciting future directions of our work.”

Much work stays to translate these latest findings into practical devices, Soljačić cautions. It could take some years to develop the obligatory interfaces between the optical and electronic components and easy methods to connect them on a single chip, and to develop the obligatory on-chip electron source producing a continuous wavefront, amongst other challenges.

“The explanation that is exciting,” Roques-Carmes adds, “is because this is sort of a special kind of source.” While most technologies for generating light are restricted to very specific ranges of color or wavelength, and “it’s normally difficult to maneuver that emission frequency. Here it’s completely tunable. Just by changing the rate of the electrons, you’ll be able to change the emission frequency. … That excites us in regards to the potential of those sources. Because they’re different, they provide latest sorts of opportunities.”

But, Soljačić concludes, “to ensure that them to grow to be truly competitive with other sorts of sources, I feel it’ll require some more years of research. I might say that with some serious effort, in two to 5 years they could start competing in no less than some areas of radiation.”

The research team also included Steven Kooi at MIT’s Institute for Soldier Nanotechnologies, Haoning Tang and Eric Mazur at Harvard University, Justin Beroz at MIT, and Ido Kaminer at Technion-Israel Institute of Technology. The work was supported by the U.S. Army Research Office through the Institute for Soldier Nanotechnologies, the U.S. Air Force Office of Scientific Research, and the U.S. Office of Naval Research.


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