Interpretation of Rings in the Far-Field Pattern of Optical Masers

Abstract

It has been believed that the interference rings in the far-field pattern of the radiation of an optical maser is due to the oscillations in off-axis modes. It is shown here that the rings in the far-field pattern are produced by the interference of radiations from atoms in a filamentary region of oscillation with an axial mode. The angle of maximum intensity for the m-th order interference is approximated by µθ _m =(µλ/L)^½(m+1/2)^½, m=1, 2, … and the zero-th order appears in a direction θ₀=0. Here µ is the index of refraction and L is the length of the maser. The result agrees fairly well with experimental values obtained from ruby masers.