Abstract

It is well known that a broadband dye laser is extremely sensitive to small absorption losses within the laser cavity and this phenomenon forms the basis for intracavity absorption spectroscopy. In a similar fashion, introduction of small optical gains into the laser cavity results in the laser locking onto wavelengths corresponding to these small gains. This internal gain injection locking leads to a method for (1) sensitive detection of small optical gains, and (2) specific state preparation for spectroscopic or chemical dynamic studies. A particularly attractive feature of this technique is that it is not necessary to know the wavelength where gain occurs before the measurement because the dye laser automatically finds the correct wavelength. Optical pumping with radiation from an external Ar⁺ laser was used to create population inversions between vibronic levels in molecular I₂ and Br₂ samples placed inside the cavity of a cw dye laser. We are able to detect optical gains as small as 2 × 10⁻⁵ on transitions between states in these molecules. By tuning the Lyot filter we are able to selectively populate specific, high-lying vibrational levels of the ground electronic state of both I₂ and Br₂. The internal injection resulted in the first reported cw lasing of Br₂ in the visible spectral region.

© 1985 Optical Society of America