Re: added laser cutter to my mill (pics)

Excellent post Tom, thanks! (Are you an optics guy? You sound like
it!)

I am seeing pretty much exactly what you described. A focused spot
of about 0.012 inches and a depth of focus of at least 1/4 inch. I
am not sure the Synrad laser M^2 value is 1...might be 1.1 or
something.

The formula I found for focus spot size is:

spot dia. = 1.27 * f * wavelength * M2 / D

Or for CO2 lasers in particular:

spot dia. (in mm) = 0.013 x M2 x f / D

Where f is the focal length of the lens and D is the diameter of the
beam entering the lens.

So, for my 3 inch focal length lens if the beam is about 4mm, then
the spot dia = 0.25mm = 0.0098 inches, assuming M^2 = 1, which it
probably doesn't. The only thing I can control with my existing
parts is the Diameter of the laser beam by moving it farther from the
lens, right? Increasing D will decrease my spot size.

Thanks again for the explanations.

Rick