Discrimination Against Unwanted Orders in the Fabry-Perot Resonator

It is proposed here that the usual Fabry-Perot interferometer structure of the optical maser may be modified in a very simple way to provide discrimination against unwanted orders. The modification is an extra reflecting surface suitably positioned outside the maser which can greatly affect the losses of the various orders. A simple one-dimensional analysis is given for the effect, and numerical results are presented for a realistic case, showing that the effect can be large. It is concluded that this technique may be useful in preventing unwanted oscillations in the optical maser.