Small Ammonia Gas Concentration Detection By Spherical Optical Microsphere

Spherical microresonators based on whispering gallery modes (WGM) have been used for measuring the concentration of ammonia vapours. Because of their high Q-factors, the WGM microresonators are very sensitive to environmental conditions such as temperature, pressure and moisture. Adding a porous layer of silica (SiO2) onto the sphere's surface makes such sensors sensitive to different kinds of vapours like ethanol, ammonia, etc.