A laser cavity used as an etalon for interferometric control of its own field

A quantitative relationship between the cavity parameters and the angular structure of the emission scattered in a parallel-plane active cavity filled with an arbitrary set of optical elements has been determined. The multipath interference into the active cavity is demonstrated to have properties which differ radically from similar processes in the etalon—among other things the relatively low finesse of the cavity interference rings is independent of the mirror quality and is a function of the Fresnel number only. The use of the operating laser cavity as an etalon for precise control of its own mode wave parameters is discussed.