SPATIALLY PARTIALLY COHERENT FABRY-PEROT MODES

The recently developed coherence theory of stable laser resonators is applied to an ideal plane-parallel Fabry-Perot resonator. We make use of an explicit, integral-type, biorthogonal expansion of the exact, no n-Hermitian, scalar propagation kernel. The resonator admits various s patially partially coherent modes because of the degeneracy of the con ventional transverse modes. The spatial second-order modes of the Fabr y-Perot resonator containing only homogeneous plane waves correspond t o an eigenvalue of unity, and several types of such partially coherent modes are identified. These include the diagonal superpositions of th e coherent Fox-Li modes and the general expressions for the cross-spec tral densities associated with the propagation-invariant modes and the self-imaging modes. Some special cases are analyzed as illustrations.