Ray interference in tunable whispering gallery mode semiconductor laser

We have observed the interference of rays in a whispering gallery mode (WGM) semiconductor diode laser with a half-disk cavity. The interference leads to the formation of about 20 lobes in the radiation directivity pattern in the far field zone. Each of these lobes consists of even narrower components. It is established that the number of narrow lobes is determined by the coherent counterphase rays originating from peripheral points of the half-disk cavity mirror. The wide lobes are related to adjacent coherent radiation sources, the presence of which is confirmed by the near field pattern.