Stability of three-mode action of a jet dye laser

A jet dye laser emitted two and three modes with the same intermode frequency spacing. A Lamb analysis of the stability of three-mode lasing accounted for the simultaneous generation of side modes, coincident spatially in the active medium. This lasing was attributed to the influence, which weakened mode competition, of combination tones when beats between the adjacent modes were in phase with the central mode. Fluctuations of the frequency of these beats observed experimentally were an order of magnitude weaker than in the two-mode case.