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.
The quality of the output signal of the laser gyro is closely related to the loss of the high mirror. At present, the research on the total loss of the high-reflection film has been quite perfect. In order to further study the optical properties of the high-reflection film, the total loss of the high-reflection film can be refined into three parts: transmission loss, scattering loss and absorption loss. Starting from the current research situation at home and abroad, this paper mainly introduces three methods, including spectrophotometer method, DF transflectometer and cavity ring-down technique, and discusses the measurement principles of these three methods. The development status and accuracy level of transmittance measurement technology, and the advantages and disadvantages of these three methods are analyzed, and the methods to improve the measurement accuracy and the possible development direction in the future are pointed out. Finally, other common methods of transmittance and reflectance measurement and the corresponding measurement accuracy are introduced.
In recent years, with the development of ultra-smooth surface polishing technology and extremely low-loss coating technology, the reflectivity of high-reflectivity mirror has become higher and higher, and the loss has become lower and lower. The high-reflectivity mirrors with total loss below 10-5 Even 10-6 have been commercialized. At the same time, measurement methods for the loss of high-reflectivity mirrors are constantly evolving. This article summarizes the loss measurement methods for high-reflectivity mirrors and the latest research progress at home and abroad, gives the principle of mainstream methods for high-reflectivity mirrors loss measurement, and introduces the measurement method for total loss and the various individual loss which make up it, including scatter, absorption and transmissions loss. What’s more, corresponding advantages and disadvantages are summarized.
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