Nanoliter‐Scale Light–Matter Interaction in a Fiber‐Tip Cavity Enables Sensitive Photothermal Gas Detection

Author:

Yan Yue1,Xiao Xunzhou1,Nie Qinxue1,Wang Zhen1,Chen Yifan2,Wu Jiahao2,Zhou Nansen3,Zhou Renjie3,Yang Sen2,Ren Wei1ORCID

Affiliation:

1. Department of Mechanical and Automation Engineering The Chinese University of Hong Kong Hong Kong SAR China

2. Department of Physics The Hong Kong University of Science and Technology Hong Kong SAR China

3. Department of Biomedical Engineering The Chinese University of Hong Kong Hong Kong SAR China

Abstract

AbstractLaser spectroscopy offers a significant tool for revealing specific molecular details with the desired accuracy and sensitivity. However, it poses challenges to maintain high sensitivity when targeting a micro‐region. Here, a dual‐enhanced photothermal approach is presented using a high‐finesse fiber Fabry–Pérot (F–P) cavity, tailored for highly sensitive chemical sensing with nanoliter‐scale light–matter interaction. A spheric surface (diameter: 50 µm, radius of curvature: 910 µm) is created on the fiber tip using focused ion beam milling. By adding a high‐reflectivity dielectric coating to the spheric surface, a fiber F–P cavity is obtained with a length of 473 µm and a finesse exceeding 4000. The intra‐cavity pump light within the gas‐filled fiber cavity generates a strong photothermal effect upon gas absorption. This effect induces phase modulation, which is amplified and detected by coupling a probe laser to the fiber cavity‐based interferometer. A minimum detection limit of 10 parts‐per‐billion (ppb) of C2H2 at 1530.37 nm is demonstrated using only 1 mW of pump power, corresponding to a normalized noise equivalent absorption coefficient of 9.1×10−11 cm−1∙W∙Hz−1/2. This platform breaks the bottleneck of ultrasensitive gas detection with a very short light–matter interaction length, promising significant advancements in microscale chemical analysis through optical investigations.

Funder

National Natural Science Foundation of China

Innovation and Technology Commission - Hong Kong

University Grants Committee

Publisher

Wiley

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