Design considerations for mode selective Fabry-Perot laser resonator

A theory of mode selective multireflector Fabry-Perot laser resonators is developed, and a practical design problem to achieve the maximum discrimination against unwanted modes is solved. The laser resonators under consideration are expressed entirely in terms of an equivalent electric Circuit and treated mathematically on the basis of classical circuit theory. The expression determining both the oscillation frequencies and the minimum gain required to maintain steady oscillations are derived. The effects of mirror spacing and reflectivities on mode selectivity are shown. A numerical example shows that a helium-neon gas laser consisting of a four-reflector resonator can exhibit an appreciable suppression of spurious oscillations in all unwanted axial modes by suitable choice of parameters.