Power dependence of continuous-wave intracavity spectroscopy

A theoretical and experimental analysis of the mode structure of a cw dye laser is presented that explains the increase in sensitivity enhancement of cw intracavity dye-laser spectroscopy (IDLS) at low power. We propose that this high sensitivity is associated with a long mode lifetime, in analogy to pulsed IDLS, in which high sensitivity is associated with a long pulse duration. A numerical solution of the laser rate equations (including spatial inhomogeneity) shows that a long mode lifetime can be achieved when few modes are lasing. Experiments show that this condition exists only at low power.