Enhancement of Absorption Spectra by Dye-Laser Quenching*

Abstract

A new technique has been developed to enhance the detection of absorption spectra of weak absorbers. Preliminary experiments, which illustrate the technique, are described. An organic-dye laser normally emits a continuous spectrum with a bandwidth of 2–10 nm. The effect of placing an absorbing-gas sample inside a dye-laser cavity results in laser quenching at those wavelengths where the sample absorption exceeds a minimum threshold absorption. The threshold for absorption quenching appears to be very low; absorption of the order of 0.5% can cause spoiling of laser action at the absorbing wavelengths and displacement of laser emission to wavelengths where absorption is below the critical switching level. Detection limits for atoms and molecules by means of absorption spectroscopy inside a laser cavity can be more than two orders of magnitude lower than those attainable through conventional absorption spectroscopy. Experiments with I₂ and sodium both inside and outside the cavity of a rhodamine 6-G laser are described. A qualitative consideration of the proposed mechanism indicates that the technique can be significantly improved with further development.