We investigate the evolution of continuous-wave laser oscillation from free-running to mode-locked operation assuming a nonlinear device with an intensity-dependent transmittivity or reflectivity to be the mode-locking element. An intensity threshold for self-starting passive mode locking is predicted and related to the linewidth of the first beat note of the power spectrum of the free-running laser output. Experimental results confirm the predictions of the theory.
© 1991 Optical Society of America
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