Editing Beam diameter (section)

==Measurement==
International standard ISO 11146-1:2005 specifies methods for measuring beam widths (diameters), [[beam divergence|divergence angles]] and beam propagation ratios of laser beams (if the beam is stigmatic) and for general astigmatic beams ISO 11146-2 is applicable.<ref name="11146-1">ISO 11146-1:2005(E), "Lasers and laser-related equipment — Test methods for laser beam widths, divergence angles and beam propagation ratios — Part 1: Stigmatic and simple astigmatic beams."</ref><ref name="11146-2">ISO 11146-2:2005(E), "Lasers and laser-related equipment — Test methods for laser beam widths, divergence angles and beam propagation ratios — Part 2: General astigmatic beams."</ref> The D4σ beam width is the ISO standard definition and the measurement of the [[Beam parameter product|M<sup>2</sup> beam quality parameter]] requires the measurement of the D4σ widths.<ref name="11146-1"/><ref name="11146-2"/><ref>ISO 11146-3:2005(E), "Lasers and laser-related equipment — Test methods for laser beam widths, divergence angles and beam propagation ratios — Part 3: Intrinsic and geometrical laser beam classification, propagation and details of test methods."</ref>

The other definitions provide complementary information to the D4σ. The D4σ and knife-edge widths are sensitive to the baseline value, whereas the 1/e<sup>2</sup> 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]].