I have a 90W RECI CO2 laser tube that I recently measured the beam divergence on. This was done by pointing the laser at a fire brick and melting it for a few seconds at different distances. Multiple samples were taken and the glassed area was measured with calipers and averaged. (please advise if you know of a better method)
Diameter at 3ft: 4.7mm
Diameter at 12ft: 6.8mm
Diameter at 38ft: ~21.0mm (not reliable data)
I am planning to build a CNC gantry system with mirrors and a stationary laser. It will require 17ft maximum beam distance and 2ft minimum beam distance. The layout is similar to this image; where the laser does not go through any optics until right before the cut. My focusing lens has a 127mm EFL and its distance from the cut will remain constant. The beam size will not exceed the mirror or optics diameter, but I believe the changing angle of divergence will change my focal point at different locations on the XY bed.
How can this be corrected for or minimized? I noticed that most CO2 cutter bed sizes are small; is that the only way to minimize this issue?
I am attempting to understand the equations on page 5 (Propagation Characteristics of Laser Beams) of Laser Principle Basics.
I since the angle of the outside of the beam (labeled "irradiance surface") is different at A1, A2, and A3, the focus points at F1, F2, and F3 would be different respectively. F1 would have the shortest focus length, and F3 (say 17ft away) would have the longest focus length.
Based on the shape of this pseduo graph; I would infer that the divergence error between F1 and F2 would be greater than the divergence error between F2 and F3.
Is this correct? Or are there other distance related issues I am not considering?
Also, do different qualities of CO2 laser tubes have different rates of divergence or am I up against pure physics here?