Frequency tunable laser closes in on terahertz gap

While electronic oscillators, such as the ones commonly used in radio transmitters, can reach frequencies up to 0.3 terahertz with a relatively good efficiency and optical devices like lasers work well starting at about 3 THz, it is difficult to create sources bridging the terahertz gap between the two domains.

Terahertz sources can be used in security imaging, and materials have widespread responses at those frequencies. Some plastics, for example, are nearly transparent.

Amirzhan et al. developed a quantum cascade laser-pumped molecular laser that is frequency tunable across at least 120 lines within the terahertz gap.

The key element of the system is the methyl fluoride gain medium, which absorbs incoming infrared radiation from a quantum cascade laser and converts it to terahertz frequencies. This is due to the molecule’s large permanent dipole moment, which makes it naturally and strongly interact with light.

“We get this very wide tunability, because we are able to get the laser emission from any of the rotational lines of the methyl fluoride molecule,” said author Paul Chevalier.

The team evaluated the laser’s performance in comparison to models. While the power is currently in the microwatts, they expect to improve the efficiency to operate at a milliwatt. The researchers aim to make the source even more compact, with the eventual goal to fit the entire system inside a shoebox.

“It is complicated to make these devices efficient and portable,” said Chevalier. “This is where our technology really has the potential to make a difference, because we can make it small, portable, and tunable in frequency.”

Source: “A quantum cascade laser-pumped molecular laser tunable over 1 THz,” by Arman Amirzhan, Paul Chevalier, Jeremy Rowlette, H. Ted Stinson, Michael Pushkarsky, Timothy Day, Henry O. Everitt, and Federico Capasso, APL Photonics (2022). The article can be accessed at https://doi.org/10.1063/5.0076310 .