Abstract

Ultrasensitive detection of volatile organic compounds (VOCs) is pivotal for early disease diagnosis and industrial safety, yet existing photoacoustic spectroscopy (PAS) systems struggle to breach the sub-ppb barrier required for practical applications. Here, we overcome this limitation by demonstrating a PAS architecture driven by a gain-switched Er3+/Dy3+ co-doped mid-infrared fiber laser, achieving an unprecedented detection limit of 416 ppt for propane, which is an order-of-magnitude improvement over state-of-the-art systems.

This performance arises from a direct pump-modulation strategy that generates high-energy microsecond pulses to significantly enhance photoacoustic excitation without power loss. Crucially, the laser's broad tunability (3.2–3.55 μm) covers the fundamental C-H stretching band, enabling not only high-resolution spectral reconstruction but also the versatile detection of multiple disease markers and industrial hazards, including isoprene (cardiovascular biomarker), 1,2-dimethoxyethane (battery failure indicator), and propanal (food safety marker).

By delivering clinical-grade sensitivity in a compact, robust fiber-based format, this work establishes a transformative pathway toward deployable, high-performance gas sensing solutions.