Evanescent Wave Lab‐on‐Fiber for High Sensitivity Gas Spectroscopy with Wide Dynamic Range and Long‐Term Stability.

Micro/nano waveguide has been widely exploited for gas sensing due to its strong confinement of evanescent field, compact size, and fast response. However, the state‐or‐the‐art evanescent‐wave gas sensors still struggle to satisfy the requirements of high sensitivity, high selectivity, large dynamic range, and long‐term stability. In this work, microfiber‐based evanescent‐wave mode‐phase‐difference photothermal spectroscopy for trace gas detection is reported. With a microfiber of 5.6 cm in length and 2.36 µm in diameter, noise‐equivalent‐concentration of 160 ppb methane in nitrogen is achieved with a dynamic range over 6 orders of magnitude, response time of less than 6 s, and <3% instability over 7 days. The technique utilizes commercial fiber‐optic components to make cost‐effective lab‐on‐fiber probes with real‐time and remote detection capability for industrial, medical, and environmental monitoring. [ABSTRACT FROM AUTHOR]