Harvard University and TU Wien have built a new miniature racetrack-shaped laser. The device produces a stable frequency comb in the mid-infrared. This could pack a lab‑sized gas spectrometer onto a single microchip.
The laser was developed by applied physicists at Harvard’s School of Engineering and TU Wien. Federico Capasso, the Robert L. Wallace Professor of Applied Physics, led the work with co‑senior author Benedikt Schwarz. The first authors are Ted Letsou and Johannes Fuchsberger. The study appears in Optica.
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Frequency combs are lasers that emit hundreds of evenly spaced colors of light. They are used in high‑precision measurements. But making them bright, stable, and small has always been hard. Traditional lasers need bulky stabilizing equipment.
The new device is a quantum cascade laser redesigned as an optical ring resonator. Light races around the loop 15 billion times per second. The team drives the laser with a radio‑frequency signal that matches the light’s round‑trip speed. This snaps the laser into a stable comb locked to the electronic signal.
This laser could be used in dual‑comb spectrometers. These instruments measure gases like carbon dioxide and methane by combining two combs. But standard combs are sensitive to stray reflections. Even a small mirror can destroy them.
The work is still in the lab. Multiple racetrack lasers must be patterned side‑by‑side on a single chip to build a full dual‑comb sensor. That step is next.
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A tiny, feedback‑immune comb enables portable gas sensors for greenhouses, factories, or even breath analysis. The racetrack design forces light to travel only one way. Reflected light dies out instead of breaking the comb. This clears a major hurdle toward chip‑scale medical and environmental diagnostics.
