to the D4σ. The D4σ and knife-edge widths are sensitive to the baseline value, whereas the 1/e2 and FWHM widths are not. The fraction of total beam power encompassed by the beam width depends on which definition is used. The width of laser beams can be measured by capturing an image on a camera, or by using a laser beam profiler. See also Beam waist Fresnel zone References Antennas (radio) Optics