 a transverse mode of a beam of electromagnetic radiation is a particular electromagnetic field pattern of radiation measured in a plane perpendicular (i.e., transverse) to the propagation direction of the beam. transverse modes occur in radio waves and microwaves confined to a waveguide, and also in light waves in an optical fiber and in a laser's optical resonator."transverse electromagnetic mode" transverse modes occur because of boundary conditions imposed on the wave by the waveguide. for example, a radio wave in a hollow metal waveguide must have zero tangential electric field amplitude at the walls of the waveguide, so the transverse pattern of the electric field of waves is restricted to those that fit between the walls. for this reason, the modes supported by a waveguide are quantized. the allowed modes can be found by solving maxwell's equations for the boundary conditions of a given waveguide. ==types of modes== unguided electromagnetic waves in free space, or in a bulk isotropic dielectric, can be described as a superposition of plane waves; these can be described as tem modes as defined below. however in any sort of waveguide where boundary conditions are imposed by a physical structure, a wave of a particular frequency can be described in terms of a transverse mode (or superposition of such modes). these modes generally follow different propagation constants. when two or more modes have an identical propagation constant along the waveguide, then there is more than one modal decomposition possible in order to describe a wave with that propagation constant (for instance, a non-central gaussian laser mode can be equivalently described as a superposition of hermite-gaussian modes or laguerre-gaussian modes which are described below). modes in waveguides can be further classified as follows: *transverse electromagnetic (tem) modes: neither electric nor magnetic field in the direction of propagation. *transverse electric (te) modes: no electric field in the direction of propagation. these are sometimes called h modes because there is only a magnetic field along the direction of propagation (h is the conventional symbol for magnetic field). *transverse magnetic (tm) modes: no magnetic field in the direction of propagation. these are sometimes called e modes because there is only an electric field along the direction of propagation. *hybrid modes: non-zero electric and magnetic fields in the direction of propagation. hollow metallic waveguides filled with a homogeneous, isotropic material (usually air) support te and tm modes but not the tem mode. in [[coaxial ca
Electromagnetic_radiation Laser_science Wave_mechanics