Mounting tube- what distances from mirror?

[injunear]

I was wondering if there's a minimum distance to avoid when positioning the output of my 80 watt tube to the first mirror. One would think the closer the better (for aim) but I always see a few inches distance between the two. Is this distance to prevent heat from building in the mirror itself?
My tube's long and I would like to minimize the 'stick out' on the right side of the cabinet.

Now that I have your attention, a second question would be: assuming there's a minimum distance not to exceed, what effect would placing a combiner equidistant between the output of the tube and the first mirror, with the tube and first mirror set to 'X' minimum distance?

Thanks
Bob T.

[TrickyCNC]

mine is approx 1" front the tube end to the mirror housing.

1 to 2" should be fine. access to clean the mirror and opto coupler is a good thing ! .. for the opto coupler, (in the en of the tube) a 'bent' cotton bud stick is a good option

don't forget to check the beam alignment all the way through if you move the tube

[injunear]

Thanks....I'll go with 2"~3 inches between the first mirror and the tube lens and try to fit the combiner lens in between.

Bob T.

[TLHarrell]

There is no minimum distance at all, except for being able to actually fit your hardware into the space. The beam won't get mad if it's hit a mirror 1/4" too soon. Only thing is making sure you have space for adjustments and cleaning.

[injunear]

There is no minimum distance at all, except for being able to actually fit your hardware into the space. The beam won't get mad if it's hit a mirror 1/4" too soon. Only thing is making sure you have space for adjustments and cleaning.

Yes, I know. My only concern was heat buildup in the mirror. I'm sure these mirrors aren't 100% efficient in reflectivity and the losses could be dissipated in heat within the glass itself? Just speculation as I really haven't looked up the efficiency of the mirrors themselves, if they spec them.
If it's negligible then I won't worry.

Thanks
Bob T.

[TLHarrell]

If your mirror is absorbing heat, you've got some serious problems. There is no issue with heat buildup in the mirrors as all but the most miniscule bit of the laser energy is reflected. Anything else is due to a dirty mirror. It is of no concern at the laser powers we are dealing with.

Now, if you're building a 3,000 watt commercial laser from scratch, yes we'd have to deal with that possibility.