Detection of chemicals in a sample.

摘要

A semiconductor laser power build-up system includes a semi-conductor laser (110). An optical resonance cavity is defined between at least two reflective elements (120; 310; 410 and 122, 124, respectively) and has an intracavity light beam (126) along an intracavity beam path. A return light beam (136), which is a portion of the intracavity light beam, is transmitted through one of the reflective elements and is coincident with but oppositely directed relative to the incident beam. The laser is wholly optically locked to the cavity and the intracavity beam passes substantially without loss within the cavity. In a preferred application, a sample is placed in the cavity and a detector (130) is provided to sense chemicals in the sample by, for example, detecting Raman-scattered light. A wavelength-determining element (118) such as a grating or an etalon is preferably in the incident beam path between the laser and the cavity. The reflective elements can have very low transmission losses, an emission facet of the laser can have very low reflectivity, and feedback into the laser may be strong, for example, above 3%. When the laser is a diode laser, the invention provides for driving the diode laser with a current that is less than its bare-diode threshold current.