GaAs lens selection?

I’ve noted that some posts elsewhere on the world wide interweb reference a GaAs lens for CO2 laser use. The posts seem to indicate an improvement in performance, often a goal for me, so I checked out the offerings.

Some sites are just declarative, providing specifications, costs, etc, while at least one other suggests that laser power of 100 Watts to 180 Watts is optimum for this type of lens.

Why would a lens “require” a higher power? What happens if one uses a lens in a 60 Watt machine?

Does anyone have experience with this type of lens?

GaAs lens have a different refractive index that the glass lens’ The same focal length lens in a GaAs will be almost flat compared to it’s glass counterpart. I have to set them on a flat surface to figure out the curve of the lens. Russ loves his for thick cutting, and my initial usage agrees that with the flatter lens you are getting more ‘central power’ out of the lens and deeper / cleaner cutting in thick material. I have begun using the GaAs lens’ for thick cutting and am so far very impressed. BTW, I have an 80W machine, he uses his in anything from a 50W to a 70W. It’s not the wattage, but what the lens can do with it that seems to make the difference.

I don’t think the existing lenses in a CO2 laser are glass. After all, glass engraves pretty well when hit with the IR from the tube. I’ve forgotten what the composition is for the “typical” lens, but most certainly not glass.

I suppose that the best thing for me is to buy one and see where it takes me.

You are probably right about the PVD and CVD lens’, but they are brittle and break like glass. At least you can see through them, and beam combiners will project through them. GaAs lens’ are opaque to visible light, so no red beam combiners.

I am 100% serious about the curvature. The PVD and CVD lens’ have an obvious curve to them, and it can be seen and felt. The GaAs lens have almost no curve to them. Even the 4" I had to put on my desk to know what side was up. At first glance they look like a dark gray metal disk.

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To my knowledge, there are not many options of what material you can produce optical lenses from. Glass, plastic, crystal (including diamond ;-), are probably the only materials for the purpose. Do you have anything else in mind, what material could be used?

As I understand it, the material used for a CO2 lens needs to have low IR absorption and good thermal conductivity. Zinc selenide and germanium meet these criteria, as does gallium arsenide but that’s toxic. Germanium has higher IR absorption than zinc selenide and as such is more suitable for low power devices, but it also has a higher index of refraction which reduces spherical aberration. Apparently, sodium chloride can also focus IR and can tolerate a lot of heat but it needs a dry environment.

I must have misunderstood the post. I have read it as it is the lens material it is about. The coating itself can, as you describe, be many materials. However, if you have an optically bad lens with small inclusions or when the optical and mechanical axis is not lying perfectly on top of each other, then all the fine coatings do not help.