Longitudinal mode selection in lasers with three-mirror reflectors

The complex reflectance of a combination of three parallel mirrors with arbitrary distances is computed. If the distance between the mirrors is equal to an integer multiple of a certain wavelength of the incident light, the reflectance of the system has narrow maxima and broad minima as a function of wavelength. This behavior is opposite to a usual two-mirror Fabry-Perot interferometer. It is suggested that such a combination of three mirrors as a mode selective laser reflector be used. Compared with other mode selecting devices this arrangement should be simpler in construction and should have better mode selective properties.