Phase and amplitude fluctuations in a mode-locked laser

Comparisons are made of the phase and amplitude fluctuations of a laser when it operates single mode and when it is mode locked with the same total average power. Despite the much lower signal-to- (spontaneous emission) noise ratio of the mode-locked laser, the linewidth of each of the locked modes is the same as that of the single mode. The fluctuation of the total intensity of the mode-locked laser, and the linewidth enhancement factor due to intensity fluctuation as recently analyzed by Henry, are the same in both cases.