Congratulations to Emma Bartelsen and the team members in the Caldwell lab. Emma’s paper published in ACS Photonics “Multiresonant Nondispersive Infrared Gas Sensing: Breaking the Selectivity and Sensitivity Trade-Off,鈥� has been selected as a VINSE Spotlight publication.
This work demonstrates a new approach to non-dispersive infrared (NDIR) gas sensing using wavelength-selective thermal emitters designed to overcome the traditional sensitivity鈥搒electivity tradeoff. Conventional NDIR sensors rely on broadband sources and narrowband optical filters, where increasing sensitivity often requires widening the spectral passband at the expense of selectivity. In this work, we instead engineer multi-resonant thermal emitters using aperiodic distributed Bragg reflectors (a-DBRs) designed using an inverse design framework based on the transfer matrix method and stochastic gradient optimization聽to produce spectrally selective emission at multiple molecular vibrational bands. These emitters enable filterless sensing by directly tailoring the emission spectrum to target gas absorption features. Experimental validation demonstrates enhanced detection sensitivity by simultaneously probing multiple absorption modes of propane, while selectivity is demonstrated through highly selective single-frequency emitters targeting carbon monoxide and carbon dioxide that exhibit high quality factors and no spectral crosstalk.聽These results show that optimized multi-resonant emitters can break the conventional NDIR sensitivity鈥搒electivity tradeoff, providing a pathway toward compact, filterless, and highly selective infrared gas sensing platforms.
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Authors: Emma R. Bartelsen, J. Ryan Nolen, Christopher R. Gubbin, Mingze He, Ryan W. Spangler, Joshua Nordlander, Cassandra L. Bogh, Katja Diaz-Granados, Simone De Liberato, Jon-Paul Maria, James R. McBride, Joshua D. Caldwell
Abstract: In applications such as atmospheric monitoring of greenhouse gases and pollutants, the detection and identification of trace concentrations of harmful gases is commonly achieved using nondispersive infrared (NDIR) sensors. These devices typically employ a broadband infrared emitter, thermopile detector, and spectrally selective bandpass filter tuned to the vibrational resonance of the target analyte. However, fabrication of these filters is costly and limited to a single frequency. This limitation introduces a fundamental trade-off, as broadening the optical passband width enhances sensitivity but compromises selectivity, whereas narrowing improves selectivity at the expense of sensitivity. In this work, we validate a filterless NDIR gas sensing approach utilizing a multipeak thermal emitter developed through an inverse design. This emitter enhances detection sensitivity by simultaneously targeting multiple absorption bands, demonstrated through the creation of a sensor designed for the C鈥揌 vibrational modes of propane (C3H8). Additionally, a second set of single-peak emitters was developed to showcase the capability of designing highly selective sensors operating within close spectral proximity. These emitters, targeting the stretching modes of carbon monoxide (CO) and carbon dioxide (CO2), exhibit quality factors (Q-factors) above 50 and minimal crosstalk, enabling accurate detection of the target gas without interference from gases with spectrally adjacent absorption bands. This is enabled by aperiodic distributed Bragg reflectors (a-DBRs), which achieve higher Q-factors with fewer layers than periodic Bragg reflectors. Experimental results demonstrate that this approach breaks the trade-off between sensitivity and selectivity.