Nine-decade hydrogen sensing by a laser-tagging high-Q microcavity

A high-Q optofluidic microcavity with real-time resonance tracking by laser-tagging enables hydrogen detection across a nine-decade concentration range via thermal phonon transfer.

Optical microcavities offer exceptional sensitivity for gas sensing, yet they typically suffer from a fundamental trade-off between sensitivity and dynamic range. Now, Yan-Hong Guo and colleagues at University of Electronic Science and Technology of China and other institutions introduced a laser-tagging optofluidic microcavity that breaks this limitation, enabling hydrogen detection across a nine-decade concentration range [1].

The key innovative design is a Pt/WO₃ nanofilm coated on the inner surface of a hollow whispering-gallery-mode microcavity, while the optical field remains confined within the silica wall and therefore does not overlap with the sensitive material. This geometry preserves an ultrahigh intrinsic Q factor of 1.89×10⁹ during sensing, avoiding the optical losses that typically plague functionalized microcavities. The authors exploit the exothermic reaction of hydrogen on the Pt/WO₃ nanofilm to induce a local temperature rise, which shifts the microcavity resonance via the thermo-optic effect — a thermal phonon transfer process rather than carrier interaction — thus converting molecular binding into a measurable frequency change. To track this shift in real time, a probe laser is dynamically locked to the resonance through a feedback loop, a scheme termed “laser tagging”. This active stabilization suppresses phase noise by over three orders of magnitude and enables wide-bandwidth heterodyne demodulation.

With hertz-level frequency resolution and a measurable resonance shift up to 724.6 MHz, the sensor detects hydrogen from 3×10⁻⁵ ppm to 1.53×10⁵ ppm. Combined with lock-in amplification, the system can resolve individual molecular adsorption events down to the single-molecule level. The device also demonstrates >98% accuracy in detecting hydrogen in dissolved gas extracted from transformer oil.

This work offers a universal strategy to overcome the sensitivity–dynamic-range dilemma in optical microcavity sensing, opening new possibilities for trace-gas detection across energy, environmental monitoring and industrial safety. Its excellent selectivity, centimeter-scale footprint and plug-and-play operation further enable deployment beyond the laboratory.

References

[1] Guo , Y.H. , Tan , T. , Yuan , S.Y. Wang, Z.P. , Liu , Z.H. , Zhao , Y.Q. , Xu , Z.H. , Chang , B. , Xia , H.D. , Peng , L. , Zhao , G.M. , Zhou , H. , Wu , Y. , Li , B.W. , Rao , Y.J. , Yao , B.C. : Adaptive laser-tagging optofluidic microcavity for single-molecule hydrogen detection across a nine-decade concentration span. Nat. Photon. 20, 1075–1083(2026)

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