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发表于 2009-2-9 21:16:29
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本帖最后由 jackeewu2009 于 2009-2-9 21:17 编辑
M2, or Beam Propagation Ratio, is a value that indicates how close a laser id to being a single mode TEM00 beam. This in turn relates to how small a spot a laser can be focused.
For a laser propagating through space,the equation for the divergence,Θ,of a pure Gaussian TEM00 unfocused beam is given by
Θ00＝4λ/ЛD00
D00 is the waist size of the beam,and λ is the wavelength
Actual beams with addition mode often start with a larger beam waist,
D0,and/or have a faster divergence Θ0.In this case equation becomes
Θ0＝M24λ/ЛD0
where Θ0 and D0 are the divergence and widthe of a higher mode beam and M2 is greater than 1 and is named the "Beam Propagation Ratio" per the ISO 11146 standard.
When a pure Gaussian laser beam is focused,the width of the focused spot is defined by:
d00＝4λf/ЛD00,
where d00 is the ideal focused spot width,f is the focal length of the lens,and D00 is the width of the input beam waist and is placed one focal length from the lens as shown
When a distorted or multimode is focused ,is
d0＝M2 4λf/ЛD0 |
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