Triple-Mode Action of a Broad-Band Laser from the Viewpoint of Intracavity Frequency-Dispersion Spectroscopy

For the beat spectrum of a triple-mode dye laser, there exists a component with a frequency equal to the difference in intervals between adjacent modes. The correlated technical fluctuations of these intervals compensate each other. This experimental fact is considered as promising for the development of a new spectroscopy method with a detection limit of the order of 10-10–10-11 cm-1 with respect to absorption in the probing volume. It is based on different changes in adjacent-mode intervals due to dispersion of the resonance line of the intracavity absorber. Thus the low frequency signal appearing in the beat spectrum can be detected. The latter is proportional to the density of absorbing particles.