UCSB professor and director of the Institute for Terahertz Science and Technology Mark Sherwin and his research group recently demonstrated how the recollision of electrons produced multiple frequencies of light using high- and low-frequency lasers.

Electron-holes are created by simultaneously aiming both low- and high-frequency laser beams at gallium arsenide nanostructures, causing the electrons to be ripped from their cores, accelerated and smashed back into the cores they left behind.

The electron’s excess acceleration is used to create an electron-hole pair called an “exciton.” An exciton — the bound form of an electron and hole — is formed when a photon is absorbed by a semi-conductor leaving behind a positively charged “hole.” According to Coulomb’s law, the positively charged hole and the negatively charged electron are bound together through mutual attraction.

In the experiment, the lower frequency laser and strong terahertz field first pulls the electron away from the hole and accelerates it back toward the vacant area that the electron was originally pulled from. The extra energy is provided by the laser’s terahertz pulse which is transferred from the decelerating electron and emits photons at various frequencies.

The mixing of lasers results in electrons that emit photons in multiple frequencies, with each frequency corresponding to a different color.

To conduct this experiment, Sherwin used UCSB’s Free-Electron Laser, a building-size machine in Broida Hall. Although the size of this laser makes it impractical in some instances, it does provide an advantage in exploring the potential benefits of certain fundamental materials.

According to Justin Watts, a researcher in Sherwin’s group, this phenomenon has the potential to significantly increase the speed of data transfer as well as communication processes. Cell phones, for example, operate at 1 GHz while terahertz transmission has the potential to transfer data approximately 300 times faster.

“Creating efficient methods to generate higher frequencies by using low and easily generated frequencies could have many applications in ultra-fast communications, electronics and even medicine,” Watts said.

In a recent press release, Ben Zaks, a UCSB doctoral student in physics, compared this phenomenon to cable internet, where the bundle of fiber optics sends a pulse of 1.5 micron wavelength beams composed of various frequencies that are separated by small gaps. An even spacing of emitted pulses is essential because it decreases the chance of mixing different data that is being transferred.

“Optical data travels at the speed of light,” Watts said. “But the limiting factor is the time between packets of information sent and processed.”

According to Sherwin, the research team may provide a more comprehensive understanding of these findings and, in the future, may collaborate to advance data transfer.

“Now that we’ve seen this phenomenon, we can start doing the hard work of putting the pieces together on a chip,” Sherwin said in a recent press release.