BTW，上边提供的公式是全角的，Melles Griot文献中是半角的公式。
下来学习学习，顶！！！！！
谢谢大家的奉献！长知识了
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
D00is 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
M2,是描述的一个激光器对于TEM00的接近程度。越是TEM00，激光器聚焦性能越好。
M2大还是小，关键是你要用激光器做什么了。我认为，如果需要聚焦加工，那当然是越接近1越好，
如果用准分子激光器加工，那用平顶光斑，那M2大点还好些
我是北京先锋科技的，我们能提供全套的激光检测方案，有需要的可以找我们
www.teo.com.cn
学习了................
学习啦 谢谢各位
20# cxxjhl
大概看了一下，好像介绍的不够详细，还是没有看懂。
留个言看看效果
下来看看，谢谢楼主
以上各楼层的解说也见功底，受教匪浅