Development of fibre laser systems for ring-down and intracavity gas spectroscopy in the near-IR

We describe our progress in the development of intracavity systems with erbium fibre lasers using ring-down or intracavity laser absorption spectroscopy. Ring-down times have been extended out to several milliseconds and digital signal processing techniques introduced for removal of unwanted spectral components from the data and for display of the attenuation history. The theoretical sensitivity limits for intracavity absorption spectroscopy are discussed for a three-level laser, taking into account ground state absorption, and about three orders of magnitude enhancement in effective path length is expected. A detailed analysis has been performed on the relaxation oscillations induced during the transient operation of the laser with the aim of monitoring laser parameters and for the future development of an interrogation system for the capture of modal spectra in the presence of intracavity absorbers.