Ultra-powerful terahertz laser could beam data and explore the stars

A new laser in the terahertz frequency range could offer ultrafast communications, help power autonomous vehicles, and even map interstellar space.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences, working with MIT and the United States Army, have created a widely-tunable, compact laser that works at room temperature and runs in the terahertz range. This part of the electromagnetic spectrum, somewhere between microwaves and infrared light, has remained out of reach for laser researchers due to the complex equipment required. The research was published Thursday in the journal Science.

The breakthrough could pave the way for a number of use cases. It could improve breast and skin cancer imaging, boost airport security, and even benefit wireless communications.

“One application is ultra-high capacity optical wireless communications in situations, for example, difficult to reach by optical fibers,” Federico Capasso, co-senior author of the paper, tells Inverse. “This will be in general quite short links, say one to a few miles range, because of water absorption.”

Terahertz laser: how it works

First, a quick primer. Atoms sit at higher energy levels when excited, similar to a building’s floors. A normal gas laser holds a molecule between mirrors and excites them to bring them to a higher level. They decay when they reach the floor, fall an energy level and release a photon. This triggers more molecules to decay and creates an ongoing effect that amplifies light. Changing the energy level of the excited molecules changes the photon frequency.

One method of changing the energy levels is to use light, using a process called optical pumping. Terahertz lasers before were limited by the number of frequencies they could cover due to the limits of this process.

The team’s success is in using a quantum cascade laser, invented at Bell Labs by Capasso and his team in the 1990s. These can cover a much broader range of frequencies. They paired it with a nitrous oxide laser, also known as laughing gas.

Terahertz laser: shooting into multiple applications

Its creators list a wide variety of potential applications. One idea proposed by Capasso is short-range communications in military situations, where the high data rate could offer welcome benefits.

“In addition to the large data rate, the use of such frequencies could be useful to prevent detection by the enemy thanks to both a tunable propagation distance and a potentially more directive link than with microwave communications,” Paul Chevalier, first author of the paper, tells Inverse.

It’s not just military applications that could benefit. Civilian cars could use it to communicate with each other, relaying information about upcoming accidents or stop lights. Vehicle-to-vehicle and vehicle-to-infrasturcture is expected to play a big role in the proliferation of autonomous cars.

“This corresponds to a future where autonomous vehicles will need to coordinate with traffic lights (for example) or other vehicles when they will be able to cross a particular intersection,” Chevalier says.

One of the benefits of the creation is a team can adjust a laser’s distance thanks to water absorption in the atmosphere.

“This will allow, for example, a specific set of vehicles negotiating their way through an intersection to not be interfering with another set of vehicles located a few miles away and also negotiating their way through a different intersection using the same communication frequency,” Chevalier says.

It could also benefit astronomers observing space. Because molecules have spectral fingerprints in the terahertz frequency, such a laser could enable researchers to observe clouds of dust and gas and gain a better understanding of their properties. The laser would act as the local oscillator.

“The wide tunability of our local oscillator would permit to detect a broad range of spectral features and therefore chemical compounds,” Capasso says.

While the laser is a big breakthrough, its applications are only just getting started.