OPTICAL EXTRACTION EFFICIENCY IN LASERS WITH HIGH FRESNEL NUMBER CONFOCAL UNSTABLE RESONATORS

Using the formulation of Moore and McCarthy for the equation describing the dominant mode in a positive branch confocal unstable resonator in the geometrical optics limit and a simple two-level kinetics model, we analyze the dependence of the optical extraction efficiency (η) on resonator magnification (M), length (L), small signal gain (g0), and (nonsaturable) background absorption (α).The model has cylindrical symmetry and spatially uniform small signal gain, absorption, and index of refraction.For fixed γ ≡ g0/α and M, a value of g0L that maximizes η is found.For different γ, the maximum obtainable value of η is found to be independent of M and to depend upon γ in a simple way.© 1979 Optical Society of America.