Apparatus and Method for a Microsphere Whispering-gallery Mode Evanescent-wave Sensor

Abstract

A microsphere whispering-gallery mode evanescent-wave sensor for use in the detection and identification of atoms or molecules has been developed. In operation, the species under scrutiny is introduced proximate to a microsphere in which a whispering-gallery mode has been excited. The subject species then absorbs a portion of the microsphere's evanescent light energy at compound-specific wavelengths, which absorption is then used to detect and identify the subject species. Its concentration may be determined from the absorption signal on the light in reflection or transmission. High sensitivity in the instant invention results from the long effective absorption path length provided by the whispering-gallery mode's large Q which results in a detector that is suitable for use in trace-gas sensing. The instant microsphere detection system can rival the performance of a multipass cell and can be made part of a much more compact and rugged system. Among the many potential uses for the invention taught herein includes detection of carbon monoxide, carbon dioxide, and atmospheric trace gases such as methane and ammonia.