Spectroscopy with Interband Cascade Lasers
Optical frequency combs have unique properties making them ideal for multiplexed detection of trace molecules. They are composed of many discrete modes at regular intervals, providing broadband coverage while keeping the benefits of a continuous wave laser. We are collaborating with Dr. Mahmood Bagheri at JPL, who has developed frequency combs based on interband cascade lasers, which are chip-scale devices which operate in the CH stretching region. We are developing new cavity-enhanced direct frequency comb methods using interband cascade lasers for investigating trace species in radical reactions.
Frequency combs have applications ranging from metrology to atmospheric chemistry to the search for extraterrestrial life. These devices act as many lasers with frequencies = mfrep+ f0, where frequency frep is the frequency spacing between the comb teeth, f0 is the offset frequency, and m is an integer.
We are using novel chip-scale (4 mm2) interband cascade laser frequency combs developed at the NASA JPL Microdevices Laboratory. We couple these devices to optical cavities to improve sensitivity.
When light is at the correct frequency, the optical cavity increases the path length through the sample. Combs are a natural match for enhancement cavities because both have equally-spaced transmission spectrum. We achieved a 975X pathlength enhancement using an optical cavity.
With chip-scale combs allowing for large frep values, we can scan 50 cm-1 in 1 ms, allowing for future kinetics measurements.
L.A. Sterczewski et.al. Cavity-Enhanced Vernier Spectroscopy with a Chip-Scale Mid-Infrared Frequency Comb, ACS Photonics, 2022 https://doi.org/10.1021/acsphotonics.1c01849