Patent ID: 8659758

Claim:
A system for detecting one or more analyte species present in a gaseous or liquid medium, the system comprising: a resonant optical cavity containing said medium and having at least two cavity mirrors, one of which is a cavity coupling mirror, the cavity having a plurality of optical resonance cavity modes; a laser that emits continuous wave laser light, wherein the laser is capable of being scanned whereby a mean optical frequency of the laser is adjustable over a range of frequencies, and wherein the laser is responsive to optical feedback light emerging from the cavity; mode matching optics configured to couple the laser light to the cavity via the cavity coupling mirror; and a detector configured to measure an intensity of the intracavity optical power of light circulating in the cavity and to generate a signal representing the intracavity optical power of light circulating in the cavity wherein the transmissivity of at least one of the cavity mirrors is selected such that the intensity of the optical feedback light impinging on the laser is below a threshold intensity value so as to ensure that a frequency hold interval range of the optical frequency of the laser is smaller than a free spectral range of the cavity.