Spectral linewidths of two mode lasers
By application of quasilinear response theory the spectral linewidths of two mode lasers near their threshold are calculated. Use is made of an adaequate fluctuation-dissipation relation. The laser is described by a fluctuation Hamiltonian with intensity and phase coupling of the modes. Incidentally the two modes' intensity fluctuation linewidths (given earlier) are rederived, and a formerly given result on the detuned single mode laser is corrected. For the phase coupled two mode laser we find a third threshold between the photon thresholds and, for large pumping, a linewidth factor 1/2.