QUANTUM-NOISE ANALYSIS OF FREQUENCY-DOUBLING RING LASERS - NONLINEARITY-INDUCED NOISE ENHANCEMENT AND ITS DEPENDENCE ON GAIN PROFILE

Using a traveling-wave model that can treat the spatial evolution of l ight fields, quantum noise characteristics of frequency-doubling ring lasers are analyzed under single-frequency operation. Systems under co nsideration are the discrete system, in which a laser crystal and a no nlinear crystal are separately installed, and the self-doubling system , which is equipped with a nonlinear crystal with laser gain. It is pr edicted that the unsaturated gain profile does not affect noise charac teristics of the discrete system: nonlinear loss-induced noise enhance ment (NINE), i.e., an increase of the spontaneous emission noise assoc iated with enlarged gain that compensates the nonlinear loss, manifest s itself at a specific operating point regardless of the gain profile, In the self-doubling system, on the other hand, the manifestation of NINE will arise for higher harmonic output compared with that in the d iscrete system. For the self-doubling system, moreover, the profile of the unsaturated gain causes a significant difference in NINE; because NINE is associated with a large held variation, it is effectively sup pressed by configuring the gain profile to be flat or increasing along the direction of laser field propagation.