Carbon monoxide (CO) is an important object for atmospheric quality and medical diagnosis, and its trace concentration detection technology has been of great attention. For this purpose, various new detection methods have emerged, such as cavity ring down absorption spectroscopy and cavity enhanced absorption spectroscopy. In this paper, the demand for CO ppm-level trace concentration detection is taken as the traction, and an optical feedback cavity enhanced absorption spectroscopy system with an equivalent noise absorption sensitivity of 7.4×10-10cm-1Hz-1/2 is established to carry out the experiment of near-infrared detection of CO gas concentration. Based on the measurement data of the OF-CEAS system, the minimum measurable CO concentration of the system was inferred to be 1.98 ppm. This system can be developed as a portable respiratory gas diagnostic device and an atmospheric trace gas detection device such as NH3 and CO.
Cavity ring-down or cavity enhanced expiratory gas diagnosis is a promising technology direction in medical diagnosis, which is expected to solve the problems of rapid, accurate, non-invasive and low-cost diagnosis of some diseases. The core of these techniques for breath gas diagnosis is to use the optical resonance’s enhancement effect to increase the interaction path between laser and breathing gas, so as to improve the detection sensitivity of breathing mark gas concentration. However, in the clinical application of this kind of technology, breathing gas needs to be filled with an ultra-low loss optical resonator. In this process, the pollution of optical resonator becomes an important bottleneck that affects and restricts the development of this technology. In this paper, different from the traditional way of gas pretreatment, the ideas to solve this problem are discussed and analyzed from the perspectives of pollution discovery, structure optimization, pollution immunity design, etc. Especially, focusing on the spectral ripple effect in the optical feedback cavity enhancement system, the optimization of V-shaped cavity structure and the aerodynamic design of cavity structure, the cavity pollution problem of V-shaped cavity is discussed and analyzed. These works hope to provide some references for accelerating the clinical application of this technology.
Cavity enhanced absorption spectroscopy (CEAS) technology is one of the new types laser absorption spectroscopy technique with high sensitivity and relatively simple detection principle, which is developing rapidly and becoming more and more popular in the field of trace gas detection. A scheme of high sensitivity infrared optical feedback cavity enhanced absorption spectroscopy system is established, based on the high quality optical passive resonator made of ultralow expansion coefficient glass-ceramics, combined with the optical feedback effect of semiconductor laser which can narrow the output laser linewidth and stabilize the laser frequency. The spectral scanning of the system is realized by simultaneously scanning the cavity length of the resonator and tuning the laser current, and the spectral resolution of 0.003 cm-1 and the noise equivalent absorption sensitivity are better than 2×10-9 cm-1Hz-1/2. The system is expected to be applied to real-time analysis of respiratory gas and realize the application of the technology in human breath diagnosis.
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