Transverse mode

A transverse mode is a pattern of electromagnetic-field amplitude and phase across a laser beam’s cross-section. Cavity geometry and boundary conditions determine which patterns can persist.

Gaussian beam: A paraxial beam whose transverse field has a Gaussian amplitude profile and a curved phase front. The fundamental transverse mode of many stable laser cavities has this profile.
Longitudinal mode: A resonant standing-wave pattern along an optical cavity’s axis, associated with a discrete allowed frequency. It describes variation along the cavity, unlike a transverse mode’s cross-sectional pattern.
Laser resonator design: The design of an optical cavity to produce desired resonances, losses, and output characteristics. Resonator geometry can favor a chosen transverse mode over competing patterns.
Free-space Gaussian beam: A Gaussian-profile beam propagating without being confined by a resonant cavity. It can have a Gaussian transverse profile without being a cavity eigenmode.
Hermite–Gaussian modes: A family of paraxial beam solutions with rectangular symmetry and transverse profiles described by Hermite polynomials. These higher-order modes describe rectangularly symmetric cavity field patterns.
Polarization: The orientation and evolution of the electric-field vector of an electromagnetic wave. A transverse mode specifies spatial structure, while polarization specifies the field’s vector orientation.
Spatial filtering: The selective removal of spatial components from an optical field, often using a focus and an aperture. A spatial filter can suppress higher-order content and clean a laser beam’s transverse profile.
Geometric optics: An approximation that models light as rays and neglects diffraction and interference effects. Transverse modes require wave behavior that ray-based optics cannot describe.
Laguerre–Gaussian modes: A family of paraxial beam solutions with circular symmetry, often carrying orbital angular momentum. These modes describe circularly symmetric patterns, including doughnut-shaped intensity profiles.
Wavefront: A surface joining points of equal phase in a propagating wave. The phase structure across a transverse mode determines its wavefront shape.

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Confinement-induced resonanceBroader topic: Virtual excitation of higher transverse modes changes the effective scattering amplitude.