Chongfan Technology
News
24
2025
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03
Light Adv. Manuf. | Dancing with Light: A Wonderful 'Waltz' in Gas Sensing
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Gas sensing technology is the core of developing artificial olfactory systems and has broad application prospects. In environmental monitoring, it can monitor air quality and provide scientific basis for environmental protection policies. In the field of industrial safety, it can timely detect leaks of toxic or flammable and explosive gases, prevent industrial accidents, and ensure worker safety. Nowadays, gas sensing technology plays a crucial role in early detection and accident warning, and its importance is becoming increasingly prominent with the advancement of environmental pollution control and industrial automation safety.
Laser absorption spectroscopy is an analytical method that uses the "fingerprint" absorption characteristics of gas molecules to determine the gas composition and concentration by measuring the attenuation of the intensity of a specific wavelength laser after passing through the gas to be measured. This technology has the advantages of high sensitivity, high selectivity and non-destructive detection, and is playing an increasingly important role in the field of gas sensing. According to the Lambert-Beer law, the strength of absorbance is positively correlated with the effective interaction length between the laser and the gas. Therefore, increasing the effective absorption optical path in laser absorption spectroscopy gas sensors is an important means to improve the detection sensitivity of the system.
Optical multipass cell(multi-passcell, MPC) is an optical device used to increase the gas absorption optical path. Through a unique optical design, it guides the laser beam to reflect multiple times in a limited space, thereby significantly increasing the effective interaction length between the laser and the gas. The laser travels back and forth multiple times between the mirrors, and its trajectory forms a beautiful pattern on the lens, like the footprints of a light dancer.
Figure 1: (Cover image) Schematic diagram of light-induced thermoelastic spectroscopy based on long optical path absorption enhancement
Source: Harbin Institute of Technology
The research team established a ray tracing mathematical model based on the vector form of the law of light reflection, and based on this, designed and developed a series of dense spot optical multipass cells. These multipass cells adopt a coaxial double-spherical mirror structure, which has the advantages of low cost, stable structure, and easy adjustment of the optical path. At the same time, the optical path volume ratio is about 8 times higher than that of traditional devices. The simulation results and physical photos of the designed dense spot multi-optical path cell are shown inFigure 2as shown.
Figure 2: Simulation and physical image of dense spot optical multipass cell
The research team selected the four concentric circular spot multipass cell with the best optical path volume ratio to build a Light-induced Thermoelastic Spectroscopy (LITES) gas sensor, and achieved high-sensitivity monitoring of methane. Light-induced thermoelastic spectroscopy is a novel trace gas detection technology that has developed rapidly in recent years. This technology is based on the photothermal effect of quartz, using a small, low-cost and wavelength-non-selective tuning fork quartz crystal as a photoelectric transducer, and detecting the change in light intensity after the interaction between the laser and the target gas to realize the inversion of the target gas concentration.
The sensor system is shown inFigure 3as shown. It should be pointed out that in addition to using the above-mentioned multipass cell to provide an effective absorption path of about 38 m, this system also introduces a Raman fiber amplifier into the light-induced thermoelastic spectroscopy system, which can realize power amplification of near-infrared lasers in the 1.65 μm band and further enhance the excitation intensity. In addition, the sensing system also uses a high-performance quartz tuning fork designed by the research team to achieve efficient detection of spectral signals. With an integration time of 100 s, the minimum detection limit that the sensor can achieve is 59.5 ppb, which is comparable to similar sensors using mid-infrared light sources.
Figure 3: Schematic diagram of light-induced thermoelastic spectroscopy methane sensor
This research starts from the design of the optical multipass cell, promotes the further development of light-induced thermoelastic spectroscopy gas sensors, and achieves high-sensitivity detection of methane gas. The dazzling laser and the jumping tuning fork cooperate with each other, shining brightly in the field of gas sensing, playing a beautiful technological "waltz". It is believed that in the near future, high-sensitivity light-induced thermoelastic spectroscopy gas sensors will play a greater role in human production and life.
Paper Information
https://doi.org/10.37188/lam.2025.001
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