Technologies for detecting absorption of electromagnetic radiation traveling through a measurement volume of interest are described herein. In a general embodiment, a laser is used to emit electromagnetic radiation through the measurement volume where absorption is desirably detected. An optical collector receives a portion of the radiation and directs a first fraction of the portion back to a gain medium of the laser, where the radiation is amplified and emitted again, and directs a second fraction to an optical sensor that can detect absorption in the measurement volume based upon attenuation of energy of the radiation. As the radiation feeds back to the gain medium and is emitted again, energy at attenuated wavelengths is amplified less than at other wavelengths. Thus, attenuation of energy of the radiation due to absorption in the measurement volume is cumulative, and relatively small absorptions are amplified, allowing smaller absorptions to be detected more easily.
STATEMENT OF GOVERNMENTAL INTEREST
 This invention was developed under Contract DE-AC04-94AL85000 between Sandia Corporation and the U.S. Department of Energy. The U.S. Government has certain rights in this invention.