Intracavity linear laser spectroscopy with a frequency analytic signal

A new method of analytic laser spectroscopy is proposed. It is based on linear repulsion of the frequencies of a two-mode dye laser with an intracavity absorption cell. A demonstration experiment is reported in which a detectivity of ~ 10⁹ Hz/cm^–1 is attained. This value is less than one order of magnitude below the absolute theoretical limit. The detectivity is shown to be independent of the intensity and duration of cw lasing.