Terahertz frequency device opens large, underused region of electromagnetic spectrum

The terahertz frequency range, a currently underutilized range in the middle of the electromagnetic spectrum between microwaves and infrared light, has a lot of potential for high-bandwidth communications, ultrahigh-resolution imaging, precise long-range sensing for radio astronomy, and more. The reason that terahertz frequency devices haven’t been used as often as others is because current sources of these terahertz frequencies are large and inefficient, have limited tuning, or require low temperature operation.

As recently published in Science, we are excited to report that researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with the Massachusetts Institute of Technology and the U.S. Army, have developed a compact, room-temperature, widely tunable terahertz laser.

“This laser outperforms any existing laser source in this spectral region and opens it up, for the first time, to a broad range of applications in science and technology,” said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and co-senior author of the paper.

“There are many needs for a source like this laser, things like short-range, high-bandwidth wireless communications, very high-resolution radar, and spectroscopy,” said Henry Everitt, senior technologist with the U.S. Army CCDC Aviation & Missile Center and co-senior author of the paper. Everitt is also an adjunct professor of physics at Duke University.

While most electronic or optical terahertz sources use large, inefficient, and complex systems to produce the elusive frequencies with limited tuning range, Capasso, Everitt, and their team took a different approach.

The breakthrough of this research is that Capasso, Everitt, and their team used a highly tunable, quantum-cascade laser (QCL) as their optical pump. These powerful, portable lasers, co-invented by Capasso and his group at Bell Labs in the 1990s, are capable of efficiently producing widely tunable light.

“Molecular THz lasers pumped by a quantum-cascade laser offer high power and wide tuning range in a surprisingly compact and robust design,” said Nobel laureate Theodor Hänsch of the Max-Planck Institute for Quantum Optics in Munich, who was not involved in this research. “Such sources will unlock new applications from sensing to fundamental spectroscopy.”

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