Mode designations of laser beams

Conventionally, the resonant modes of open resonators are designated as TEM(pl). This kind of mode designation is inappropriate because of the fact that all the beam modes have at least an axial field component, the relative strength of which, in comparison with the principal transverse field components, increases with the higher-order mode numbers p and l. It is shown in this paper that the higher-order beam modes can be separated into three types of modes; namely, transverse-circular-electric modes, transverse-circular-magnetic modes, and hybrid modes. Based on this result, a new scheme of mode designations is proposed. This scheme, in fact, follows the mode designations for cylindrical dielectric (fiber and hollow) waveguide modes. Consequently, a good analogy can be obtained between the Laguerre-Gaussian beam modes and the dielectric waveguide modes, along with their common applications in optical transmission.