Lichtbündel

Lichtbündel (German for "light beam") denotes a directed collection of light rays or photons that propagate together with a defined spatial extent and direction. In optics it describes both macroscopic beams from sources such as flashlights and vehicle headlights and highly collimated beams produced by lasers. A beam may be convergent, divergent or collimated; its characteristics are described by parameters including cross-sectional intensity profile, divergence angle, spatial coherence and polarization.

In physical optics, many laser beams approximate a Gaussian intensity profile (TEM00 mode), for which beam waist, Rayleigh range and far-field divergence quantify how the beam spreads. Incoherent sources produce beams characterized by radiance and irradiance rather than fixed phase relationships. Wave optics treatments use solutions of the Helmholtz equation or paraxial approximations to model propagation, diffraction and focusing of beams.

Practical applications of Lichtbündel span illumination, imaging, optical communications, material processing, surveying and medical procedures. Beam shaping and control employ lenses, mirrors, apertures and diffractive or refractive optics to achieve desired profiles. Safety considerations are important because concentrated beams, especially lasers, can damage eyes or materials. In everyday language the term also appears in art and literature to describe visible columns of light in atmospheric conditions, where scattering by particulates renders the beam visible.