[dmauch]

What would you want in Trade or better yet how about selling me one so that you could buy more what you need than what I have for trade.
[email protected]

I have some beam combiner's I may be willing to trade for linear motion components. Drop me a line.

[tiwanacote]

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[valvolo]

I Paul,
I'm Tony from Italy.
I find your work amazing and praiseworthy, and congratulations for your patience.
thing I'm losing by dint of seeking answers to the questions on use of the laser.
through your work I get closer to understand something. thanks
one of the few things that I failed to understand is what kind of lens is that you used on your alignment device and if you can, please tell me where you found out.
thank you.
Tony

[MonoNeuron]

Hi Tony,
You can get most laser stuff on eBay now. Lens holders, mirror supports, mirrors, lenses, tubes, etc.
Just go to www.ebay.com and search for " co2 Laser " and a heap of things will come up in the list.
Rich.

[valvolo]

hi Mono!
thanks,
but i'm really a beginner in co2 so although I have seen that on ebay there are many things for the laser, I do not know specifically what to buy. my question was intended to know what kind of lens is used specifically to achieve the beam combiner for alignment and then what type of lenses used to focus the laser beam.
thanks
Tony

[MonoNeuron]

Hi Tony,
You have the choice of 2 types of lenses for focusing the beam. Gallium Arsenide (GaAs) or Zinc Selenide (ZnSe). GaAs is a harder more wear resistant material and is used where there is a chance of contamination getting back to the lens. ZnSe is much softer and also more brittle. I broke a ZnSe lens by dropping it from about 200mm onto my table.
Incidentally, the first lenses for CO2 lasers were made from salt crystals, NaCl2, or Sodium Chloride, common table salt.

GaAs won't pass the red laser pointer wavelength so is of limited use to those of us that want to see where the cutting will take place or for aligning the next cut on a used piece of material.
The beam combiner lens is usually a ZnSe flat piece that has a reflective coating on one side so the red pointer wavelength will be reflected but will also allow the CO2 wavelength to pass through.

The red pointer is set up at 45 deg to the front face of the combiner plate to reflect the pointer into the CO2 beam so it is co-incident or parallel with the beam. You usually get this setup before you start bending the co2 beam around with the mirrors which makes it so much easier because the CO2 wavelength is invisible to the naked eye.
A good starting point for a lens is about 50 mm or 2 inches focus length which gives you an all round lens with good power and small spot size and an average kerf width. The kerf is the width of the focused cutting beam and is about 0.005" - 0.004" for the 2" lens.
The smaller the focal length the smaller the spot size until you reach the limit of the wavelength to be able to be focused.

If you have a large table then you may need to install a collimating lens which increases the beam size from about 4mm to 8mm, or whatever multiplier you may have bought, so that you can focus the beam through the lens more effectively. CO2 lase beams tend to expand a bit over some distance, and is usually listed in the laser tube specs, so it throws out your focusing at the lens. Some laser tables have an automatic adjustable collimator depending on where the lens assembly is on the rails to keep the beam the right size so the focal point doesn't change.

The wider beam is more able to be focused to a smaller spot size but you also increase the kerf width and reduce the depth of field (DOF) or the allowable cutting thickness before the kerf becomes too great. What I mean to say is that the " DOF " not the kerf becomes too small. Think of the letter X as the beam and the focal point is at the middle of the X. This is the shape of the " kerf " after cutting with a small focal length. You try to strike a happy medium.

Mirrors are used to steer or bend the laser beam around corners to get to the lens assembly and each one reduces the laser power just a tiny amount because they are not 100% reflective. Somewhere around 99.6% etc. Some mirror surfaces are Gold, Aluminium, Silicon, Molybdenum and Copper. These mirrors are a bit different from "normal" mirrors in that the mirror surface is on the front of the mirror.
Copper is used as the internal reflector inside some laser tubes and they generally have a large curvature of about 2-5 meters to focus the plasma/ions/electrons/photons to the output coupler (output window) which also makes them a bit more efficient.

These are called a "first surface" mirror. If the mirror was like a normal house mirror then the laser beam would burn the glass surface before it got to the mirror surface and also refract the beam too much reducing power and altering the direction of the beam. I use cheap (free) Aluminium first surface mirrors from a photocopier for mine which work great. There is a limit to the power some of these can handle so that's why there are different types. Yag lasers have a completely different type of mirror because the YAG beam is able to cut the metal mirrors for CO2 lasers due the the different wavelength.
I hope all this helps you get to grips with a fascinating hobby/business.
Let me know if you need more info
Rich.

P.S. If I have made any mistakes here then by all means correct me. I am not a laser professional and can only comment on what I have read here and on other web sites and also from experience of about 3 years with a home built laser table.

[Tweakie]

Hey Rich,

That is just about the best introduction / description I have ever read. My congratulations on your ability to explain things.

Tweakie.