M Squared

[planters]

Been doing some research and I am finding it surprisingly difficult to relate published M squared values to practical divergence estimates. Is there a simple equation which makes this conversion (or even a reasonably close estimate)? For example, if a laser @ 532nm has a M2 of 1.05 can this be interpreted to a beam product such as ( just an example) 1mm dia. @1mrad. divergence, but if M2=1.10 then 1mmdia. @ say 1.5mrad divergence and so on? Furthermore, if the laser operates @ 640nm with the same M2 will the beam product change? And, if given a "perfect" beam with a M2 =1 what is the theoretically minimum beam product at a given wavelength?

[krazer]

Melles Griot has a few nice papers on this topic, at https://www.cvimellesgriot.com/Compa...uperGroupid=27
specifically
http://www.cvimellesgriot.com/produc...ropagation.pdf
https://www.cvimellesgriot.com/produ...easurement.pdf

If you just want to cut to the chase, the formula is given explicitly at http://www.rp-photonics.com/m2_factor.html

[planters]

Thanks. This is just what I was looking for. I am amazed at the examples in the cvimellesgriot papers as the theoretical HeNe divergence is about 1/20 of the typical divergence of our diode systems.