Development Of Ammonia Analyzer Based On Mid-infrared DFB-ICL

Ammonia(NH3)is a common toxic gas with an extremely repulsive smell.NH3 in the air can contribute to the formation of fine particulate matter(PM2.5).In addition,ammonia is a naturally occurring species in exhaled breath.Therefore,the detection of ammonia is not only important to odor and PM2.5 pollution control,but also offer a solution to diagnose and monitor a variety of medical conditions.The present paper aims to the development and optimization of mid-infrared ammonia analyzer based on TLAS with hollow waveguide.Firstly,the mid-infrared laser ammonia analyzer is designed.An overall scheme of the ammonia analyzer based on DFB-ICL with a HWG gas cell is designed.Ammonia absorption feature near 3000.3nm has been selected to avoid water vapor and carbon dioxide interference,and the function and structure of the analyzer's main modules are introduced.The system,based on HWG gas cell,has been elaborately designed considering laser coupling into the hollow waveguide and the protection for HWG.Laser coupling assembly is designed for lasers with three kinds of packages including lasers with pigtail output,TO66 and TO5 packages.Secondly,etalon effect in the laser gas analyzer is studied and two methods are applied to minimize its influence on gas detection.The first method is the optimization of modulation index based on previous studies of other researchers.And the second method is the optimization of mechanical structure after finding the mechanical distance which is relative to the etalon effect in the system.Both of the methods have greatly suppressed the etalon effect and improved SNR of the analyzer.Thirdly,the analyzer performance is tested with gas standards for the Allan variance,and the modular design is also verified.The laser ammonia analyzer developed in the paper possess high sensitivity for detecting ammonia,and the test results suggest that it can be used to detect small amount gases with fast response time.In addition,by replacing the laser source and corresponding coupling module,the system is able to measure other gases in near-infrared and mid-Infrared spectral regions.