Increasing electron-triggered light emission's intensity

A novel technique can enhance the light outputs from a particular form of electron-photon coupling, which is essential for electron microscopes and other technologies, by a factor of 100.

ANNOUNCEMENT 4-JAN-2023

 

Many contemporary technologies, like lasers, solar panels, and LEDs, depend on the way electrons and light photons interact. But due to a significant size mismatch, the interaction is essentially weak: Because an electron's wavelength is around 1,000 times bigger than that of visible light, there is a physical limit to how the two objects may interact.

Now, scientists at MIT and other institutions have developed a novel strategy to enable significantly stronger interactions between photons and electrons, resulting in a 100-fold increase in the emission of light from a phenomena known as Smith-Purcell radiation. Although it will take additional years of study to make it useful, the discovery might have consequences for both practical applications and basic scientific research.

The research was published today in the journal Nature by MIT postdocs Yi Yang (currently an assistant professor at the University of Hong Kong), Charles Roques-Carmes, MIT professors Marin Soljai and John Joannopoulos, as well as five other researchers from MIT, Technion-Israel Institute of Technology, Harvard University, and other institutions.

Using a beam of electrons and a specially created photonic crystal, which is a slab of silicon on an insulator etched with an array of nanometer-scale holes, the team discovered that they could theoretically predict stronger emission by many orders of magnitude than would typically be possible in conventional Smith-Purcell radiation. In their experimental proof-of-concept measurements, they also saw a 100-fold increase in radiation.

The free-electron-based method is fully tunable, unlike other methods for creating sources of light or other electromagnetic radiation. It can produce emissions of any desired wavelength by simply adjusting the size of the photonic structure and the speed of the electrons. This may make it particularly useful for producing sources of emission at wavelengths like terahertz waves, ultraviolet light, and X-rays that are challenging to generate efficiently.

The team has so far used a repurposed electron microscope to serve as an electron beam source to demonstrate the hundredfold improvement in emission. However, they claim that the underlying idea might possibly allow for far more significant improvements when used with equipment designed expressly for this purpose.

The method is based on the idea of flatbands, which have recently received a lot of attention in the fields of condensed matter physics and photonics but have never been used to modify the fundamental interaction between photons and free electrons. The fundamental idea is the transfer of momentum from an electron to a collection of photons, or vice versa. The photonic crystal is calibrated in a way that makes it possible to produce light at a wide variety of angles, unlike traditional light-electron interactions, which rely on creating light at a particular angle.

The same method might be applied in the reverse direction, accelerating electrons by means of resonant light waves in a manner that might be utilised to create compact particle accelerators on a chip. In the future, they could be able to carry out some tasks that at the moment need for enormous subterranean tunnels, like the 30-kilometer-wide Large Hadron Collider in Switzerland.

According to Soljai, "you could manufacture far more compact accelerators for some of the interesting applications, which would still produce highly intense electrons, if you could really put electron accelerators on a chip. Of course, that would be enormous. You wouldn't need to construct these substantial facilities for many applications.

According to Roques-Carmes, the new device could also be able to deliver a highly controlled X-ray beam for radiotherapy applications.

The device may also be used to produce many entangled photons, a quantum phenomenon that might be helpful in the development of quantum-based computing and communication systems, the researchers claim. According to Yang, "you can couple multiple photons together using electrons, which is a significantly challenging task if utilising a purely optical technique." One of our work's most interesting potential future paths is that.

Soljai warns that much work has to be done before these new discoveries can be turned into useful gadgets. Among other difficulties, developing the requisite on-chip electron source creating a continuous wavefront and the interfaces between the optical and electrical components and how to integrate them on a single chip may take some time.

Roques-Carmes continues, "The reason this is fascinating is because this is rather a distinct sort of source. While most light-generating systems are limited to fairly precise colour or wavelength ranges, changing the emission frequency is typically a challenge. It is entirely adjustable here. The emission frequency may be altered simply by altering the electrons' velocity. We are excited about these sources' potential because of it. They provide novel chances since they are unique.

However, Soljai adds, "I think it will take some more years of study for them to become fully competitive with other forms of sources. They might start competing in at least some radiation-related fields in two to five years with some real effort, in my opinion.

The study team also comprised Justin Beroz at MIT, Ido Kaminer at Technion-Israel Institute of Technology, Haoning Tang and Eric Mazur at Harvard University, and Steven Kooi at MIT's Institute for Soldier Nanotechnologies. The U.S. Office of Naval Research, the U.S. Air Force Office of Scientific Research, and the Institute for Soldier Nanotechnologies of the U.S. Army Research Office all provided funding for the project.

David L. Chandler, MIT News Office, wrote the article.