simple question - does the orientation of SI mirrors matter?

[daniel coyle]

hello, replacing Molybdenum mirrors with Silicon Mirrors. The SI mirrors have a gold and a 'not gold' side. does it matter which side faces the laser beam when I mount them?

[Rodne Gold]

Shiny Gold side to the beam..most mirrors in our level of co2 lasering are some highly polished substrate that's gold plated

[daniel coyle]

Thanks Rodne! Can I add one more hopefully short question? This is the burn pattern I get when trying to line up the first mirror with the tube (layered masking tape). I expected a dot/thick dot. Is the circular pattern normal?
268137

[Dan Hintz]

Thanks Rodne! Can I add one more hopefully short question? This is the burn pattern I get when trying to line up the first mirror with the tube (layered masking tape). I expected a dot/thick dot. Is the circular pattern normal?
268137


You'll get that pattern when the optics in a tube are out of place, or when the tube is beginning to fail...

[Rodne Gold]

We get the donut shape when pulsing a very short burst at very low power when aligning , worried me at first , but the laser works fine when running ... I checked our other tubes and they all exhibit the same or similar marks
Here's some tech stuff on laser beam shapes etc
http://en.wikipedia.org/wiki/Gaussian_beam

[daniel coyle]

Thanks Dan, Rodne

I am, in fact doing low power short pulses so that is re-assuring. I had had the laser tube checked before installing it and it had great power. Its only 4 months old. Thanks for the answers.

Dan

[Dan Hintz]

We get the donut shape when pulsing a very short burst at very low power when aligning , worried me at first , but the laser works fine when running

Makes sense, I suppose... the tubes aren't capable of handling low-power and still lasing reliably, so it would have the same effect of a misaligned tube mirror (i.e., it would have trouble lasing in that case, too).