Higher-order phase transitions in systems far from equilibrium: Multicritical points in two-mode lasers

The possibility of a system driven far from equilibrium to exhibit multicritical phenomena is discussed. As an example, the laser oscillating in two modes is shown to possess bicritical and tetracritical points depending on the strength of the coupling between the two modes. The phase diagrams indicating the regions and the nature of the four possible phases for the two-mode laser model are presented. The exponents and the scaling characteristics near the bicritical and tetracritical points are also discussed.