#  Bright, stable frequency combs enabled by racetrack quantum cascade lasers 

 





April 07, 2026

 

 

Harvard researchers and collaborators at TU Wien have developed a racetrack-shaped quantum cascade laser that generates bright, stable mid-infrared frequency combs on a chip, opening a path toward compact dual-comb spectrometers for gas sensing and industrial monitoring. The work was co-led by Ted Letsou and Johannes Fuchsberger and published in [*Optica*](https://opg.optica.org/optica/fulltext.cfm?uri=optica-13-3-533).  
  
The device uses radio-frequency injection to lock the laser into a broadband comb state. Unlike conventional straight-bar semiconductor comb lasers, the racetrack design is inherently resistant to optical feedback, a key obstacle to miniaturizing mid-infrared comb systems. In experiments, the comb remained stable even under strong reflected light.   
  
The platform could enable chip-scale tools for greenhouse gas sensing, industrial process monitoring, and medical diagnostics such as breath analysis. For more information, see the press release from Harvard [SEAS](https://seas.harvard.edu/news/racetrack-shaped-lasers-bright-stable-frequency-combs).

 ![Artistic rendering of QCL racetrack](/sites/g/files/omnuum6306/files/2026-04/onering_v19hr_1800_300dpi.png)

 

Artistic rendering by Joshua Mornhinweg.



 

 

 



 

 

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