Gas pressure effect on lens to affect focus

[JayMaechtlen]

Just food for thought -
Has anyone tested or run the numbers to see how far a lens might deflect under high gas pressure?
And, how far would that deflection move the focus point?

I wonder if that would help explain some of the rules of thumb regarding focus height when cutting various materials.
Seems like most materials that 'want' a low focus are also being cut at high pressure.

Obviously, lens diameter and thickness would affect the focus change at a given pressure.

Regards
Jay

Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[IRstuff]

Unless the gas pressure is a static pressure on the lens, which would require a sealed chamber, there wouldn't be much actual residual pressure on the lens.

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[JayMaechtlen]

The lens is at one end of a chamber, the other end has a small orifice - called the cutting nozzle.

When using Nitrogen, you're typically cutting at 2-6 bar, maybe more.
That's the static pressure in that chamber while cutting, and that's what the lens sees.
The other side of the lens is at atmospheric.

Ok, I know some systems use a window to protect the lens - depending on the design the window may or may not seal the pressure and protect the lens from it too?



Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[IRstuff]

Oh, OK, so yes, there could be some distortion of the lens, which could possibly cause a change in focus. Without knowing details about the lens, there's no way of knowing what it's sensitivity to pressure differentials might be.

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[lasermate]

According to my supplier, the lens will deflect under high gas pressure. It should change the focus position by a few microns. The material is quite rigid....

I hope this helps.

 

[Foostrap]

If using a high pressure lens, you won't have to worry about focus change due to gas pressure. If there is any change, it will be neglectable. If you don't have a high pressure lens, it could crack under pressure (20 bar).