M squared

In laser science, the parameter M2, also known as the beam propagation ratio or beam quality factor is a measure of laser beam quality. It represents the degree of variation of a beam from an ideal Gaussian beam.[1] It is calculated from the ratio of the beam parameter product (BPP) of the beam to that of a Gaussian beam with the same wavelength. It relates the beam divergence of a laser beam to the minimum focussed spot size that can be achieved. For a single mode TEM00 (Gaussian) laser beam, M2 is exactly one. Unlike the beam parameter product, M2 is unitless and does not vary with wavelength.

The M2 value for a laser beam is widely used in the laser industry as a specification, and its method of measurement is regulated as an ISO standard.[2]

  1. ^ Cite error: The named reference Siegman was invoked but never defined (see the help page).
  2. ^ "Lasers and laser-related equipment – Test methods for laser beam widths, divergence angles and beam propagation ratios". ISO Standard. 11146. 2005. {{cite journal}}: Cite journal requires |journal= (help)