This Small Business Innovation Research (SBIR) Phase I project will lead to the development of compact, low cost gas sensors and analyzers based on cavity ringdown spectroscopy using near-infrared lasers manufactured for fiber optic communications. Although conventional cavity ringdown spectroscopy can achieve part per trillion detection limits for many gases (water vapor, carbon dioxide, ammonia), few commercial applications require such extraordinary sensitivity. Instead, price and reliability are controlling factors for the sensors and analyzers market. That is why we propose a modified form of ringdown spectroscopy that should lead to low cost, compact, and rugged instruments. The Phase I effort is designed to demonstrate the effectiveness of our proposed technique which will lead to the development of a prototype instrument in Phase II.<br/><br/>Commercial applications include industrial process analysis and control, bioreactor monitoring, and worker safety. Ideally, the sensors and analyzers will be low power (possibly battery operated), self-calibrating and self-checking devices that will be sufficiently rugged to allow in situ installation.