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Simultaneous Multi-Gas Detection Made Possible With Sub-μL Samples

Simultaneous Multi-Gas Detection Made Possible With Sub-μL Samples

Simultaneous Multi-Gas Detection Made Possible With Sub-μL Samples

Simultaneous Multi-Gas Detection Made Possible With Sub-μL Samples

Credit: Marek Piwnicki/ Pexels
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Trace gas detection based on laser absorption spectroscopy (LAS) plays an important role in atmospheric monitoring, industrial emissions control, energy system and human breath analysis due to its high sensitivity and selectivity.

To date, most works were performed with a single frequency laser targeting only one species. However, the simultaneous measurement of multi-species remains a challenge to be solved especially for scenarios, where only a limited sample amount can be expected or the variation tendency of relevant species needs to be investigated.

Recently, a research group led by Prof. WANG Qiang from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS), developed a trace gas sensor with an all-fiber configuration based on photothermal spectroscopy (PTS) and frequency-division multiplexing (FDM), which is proposed for simultaneous multi-species detection. Three diode lasers with center wavelengths located at C-band, L-band and U-band are integrated to interrogate C2H2, CO2, and CH4, respectively.

Related results have been recently published in Sensors and Actuators: B. Chemical.

A pump-probe configuration is often adopted for PTS. When the wavelength-modulated pump laser is in resonance with the gas molecules, the absorption-induced phase modulation is detected by a probe-laser-based interferometer. An HCF provides a significantly increased light intensity and highly efficient light-molecule interaction within the μm-sized hollow core. To achieve multi-species detection using FDM, the wavelength of each pump laser is modulated at different frequencies for C2H2, CO2 and CH4 detection, respectively. The wavelength modulations of the pump lasers can generate separate refractive index modulation inside the HC-ARF which can be simultaneousy detected by the same probe-laser-based interferometer.

The capability of simultaneous measurement is validated by detecting the three gas species in the HC-ARF. The above figure depicts the response curves of the sensor to different mixtures of the three gas species in four successive cases, which match well with the pre-set conditions.

The linear response and the ability of simultaneous detection of the multi-species have been experimentally demonstrated. The sensor achieves minimum detection limits of 2.5 ppb, 21 ppm and 200 ppb for C2H2, CO2 and CH4, respectively, in a hollow-core fiber with a total consumption of only 0.17 μL.

Prof. Wei Ren’s group from the Chinese University of Hong Kong, Prof. Wei Jin’s group from the Hong Kong Polytechnic University, and Prof. WANG Yingying’s group from Jinan University provided strong support for this research.

With the high sensitivity, low gas consumption, compact and flexible structure, the developed gas sensor is promising in many field applications. Future work will involve the improvement of the detection sensitivity by employing longer hollow-core fiber and mid-infrared pump lasers which covers the fundamental bands of gas molecules.

Reference: Wang Z, Zhang H, Wang J, et al. Photothermal multi-species detection in a hollow-core fiber with frequency-division multiplexing. Sens. Actuators B Chem 2022;369:132333. doi: 10.1016/j.snb.2022.132333

This article has been republished from the following materials. Note: material may have been edited for length and content. For further information, please contact the cited source.