Gaussian Intensity Distribution
Gaussian Intensity Distribution (also called a Gaussian intensity profile or irradiance distribution) is the characteristic transverse intensity pattern of the fundamental (TEM₀₀) mode of a laser beam, and of idealized Gaussian beams in general.
In lasers and photonics, the optical intensity in a plane perpendicular to the propagation axis follows a smooth, bell-shaped Gaussian curve: highest on the central axis and falling off symmetrically with radial distance. Most well-designed lasers operating in the fundamental transverse mode produce beams that closely approximate this distribution.
Technical Information:
The intensity peaks on the beam axis and decreases radially according to a Gaussian function.
The beam radius is conventionally defined as the distance from the axis at which the intensity drops to about 13.5 % of its peak value; roughly 86 % of the total power is contained inside this radius.
Nearly all of the beam power lies within twice that radius.
A pure Gaussian beam keeps its Gaussian shape as it propagates in free space or passes through ideal (aberration-free) lenses; only the size of the beam and the curvature of its wavefront change.
The beam is narrowest at a location called the waist and gradually diverges beyond a characteristic distance known as the Rayleigh range.
Beam quality is commonly quantified by the M2 factor: a perfect diffraction-limited Gaussian has M2=1; real lasers have values of 1 or slightly higher (1.1–1.5 is still considered excellent TEM₀₀ quality).
Higher-order transverse modes have more complex intensity patterns that include dark nodes, but the fundamental mode is purely Gaussian.
Applications:
Laser focusing and material processing: The Gaussian profile focuses to the smallest possible diffraction-limited spot, delivering high intensity for cutting, welding, drilling, marking, and additive manufacturing. The smooth intensity roll-off is often desirable (or is deliberately converted to a flat-top profile when uniform illumination is needed).
Optical communications and free-space links: Predictable divergence and high on-axis intensity improve coupling efficiency into fibers or receivers.
Interferometry and precision metrology (including gravitational-wave detectors): Clean Gaussian modes minimize higher-order mode content and simplify cavity mode matching.
Laser diagnostics, spectroscopy, and sensing: A well-characterized intensity distribution allows accurate calculation of interaction volumes, fluence, and sampling regions.
Beam shaping and mode conversion: Gaussian beams serve as the starting point for generating flat-top, doughnut, or other custom profiles via refractive, diffractive, or spatial-light-modulator optics.
Resonator design and laser characterization: The TEM₀₀ Gaussian mode is the lowest-loss, lowest-divergence mode of stable laser cavities; M2 and intensity-profile measurements are standard quality metrics.
Gaussian intensity distribution is the ideal, most common, and theoretically simplest beam profile in laser physics and photonics, valued for its diffraction-limited focusing, shape-preserving propagation, and mathematical simplicity.