Embracing Impact: Electromagnetic Waves Clash in Direct Collisions

A research team at the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC) has shown that it is possible to manipulate photons into colliding, causing them to interact in new ways as they cross paths. 

The breakthrough occurred in the lab of Andrea Alù, Distinguished Professor and Einstein Professor of Physics at The City University of New York Graduate Center and founding director of the CUNY ASRC Photonics Initiative. It was facilitated by another recent experiment demonstrating time reflections for electromagnetic waves.

“Our work is building on a series of experiments that show how we can create metamaterials with unique properties that emerge from abrupt time variations of their electromagnetic properties. These variations allow us to manipulate wave propagation in ways not seen in nature,” said Alù. 


Typically, when two electromagnetic waves cross paths, they move right through each other without interacting. This is very different from when two massive objects, like two balls, bump into each other. In the latter case, the particles collide, and their mechanical features determine whether the energy is conserved, lost, or increased in the collision. For example, when two billiard balls collide, the total energy in the system is saved, while when two rubber balls hit, they typically lose power in the collision. While photons would be expected to go through each other without any interaction, by triggering a time interface, the scientists could demonstrate strong photon-photon interactions and control the nature of the collision.

The scientists also proposed and demonstrated an application of their concept to shape electromagnetic pulses by colliding them against each other. “This technique allows us to use an additional signal as a mold to sculpt a pulse that we are interested in structuring,” said Gengyu Xu, a postdoctoral fellow with Alù’s lab and co-leading author of the paper. “We have shown this for radio frequencies and are now working to realize this sculpting ability at higher frequencies.”

The team’s work developing methods to dictate how propagating electromagnetic waves interact and shape each other could benefit wireless communications, imaging, computing, and energy harvesting technologies, among other advances.

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