laser cutter viewing window

Hi again. I know that you need safety glasses for laser cutter. its a must. now what id like to figure out is what type of sheet of acrylic should I buy to have as a viewing window for the laser cutter I'm building. ive read that a simple piece of acrylic would do the job but id like more input from others here. is theres a # to the type of acrylic I should use specifically. my laser cutter is a 40 watt machine.

I know that a simple acrylic sheet will most likely not be sufficient. but maybe it will be. just in case I forget to put the glasses on.

... for the CO2 laser any sort of acrylic or glass is sufficient, as it's not transparent for the 10640nm wavelength of the CO2-laserbeam.

So long it's not hit with the direct beam, even a 0.2mm sheet of plastic will be sufficient.

For occasional reflection from the working area (underlying metal surfaces or such) up to the acrylic window 3mm acrylic are more than enough, as the beam is not focussed, but divergent ...

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Viktor
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Call for the project "garbage-free seas" - [reprap.org]

The 10.6µm wavelength means the light is absorbed by basically all "see through" materials out there, with the exception of some foils and materials used for CO2 laser optics.
Even clear safety goggles will do the trick, no need for special CO2 laser safety glasses at insane prices.
As VDX pointed out thickness is no issue either unless you deal with direct impcats of the laser light, refections are no problem.
One thing people seem to overlook when they start with their lasers is the problem of visible light.
The windows is there to control the work area and to protect your eyes from laser radiation.
But here it usually ends no matter what type of laser is used.
Especiall when cutting certain materials there will be more burning than vaprosing of material.
This mean there will be fire of some sort, which of course can be limited but not avaioded by air assist.
And here is the problem IMHO with CO lasers.
The generated visible light at higher power levels is limited to a very tiny spot, which means the intensitiy is high.
For this reason I actually prefer darker windows or the use of tinting foil, which in any case also takes care of any UV radiation.
Of course a 40W system won't really get into extreme dangeous levels of visible light I do recommend considering using tinted and UV protective sunglasses when observing the laser actions through a clear window.

Thats a relief! I was worried i might be wrong about what i read i will be using 3mm window since thats the smallest i found already cut to size

Those laser safe acrylic are really expensive and i was worried i would need one. Glad to know i can use regular plexiglass.

About the light emited while cutting. Ive seen that in many vids and it does look bright. Looking at that can affect vision then right? Can it be ignored or do i need glasses for that anyway? Or will darker acrlyic do just fine? I doubt UV will wholly blocked with simple acrylic unless im wrong.

... I don't think, the energy density in the spot is enough to produce ponderable UV radiation.

The visible light is essentially the evaporated material, overheated and ionized (and burning/oxidizing if evaporated without shielding gas) - but not enough energy density to create air-breakdown, what's needed, to get an UV-source ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

UV laser safety
be safe or be blind or skin scorched

Eye effects
Effects are wavelength-dependent

Ultraviolet-B+C (100 - 315 nm)
The surface of the cornea absorbs all UV of these wavelengths which produce a photokeratitis (welders flash) by a photochemical process, which cause a denaturation of proteins in the cornea. This is a temporary condition because the corneal tissues regenerate very quickly.

Ultraviolet -A (315 - 400 nm)
The cornea, lens and aqueous humour allow Ultraviolet radiation of these wavelengths and the principal absorber is the lens. Photochemical processes denature proteins in the lens resulting in the formation of cataracts.


Effects to skin
To the skin, UV-A (0.315 µm-0.400 µm) can cause hyperpigmentation and erythema. UV-B and UV-C, often collectively referred to as "actinic UV," can cause erythema and blistering, as they are absorbed in the epidermis. UV-B is a component of sunlight that is thought to have carcinogenic effects on the skin. Exposure in the UV-B range is most injurious to skin. In addition to thermal injury caused by ultraviolet energy, there is the possibility of radiation carcinogenesis from UV-B (280 nm - 315 nm) either directly on DNA or from effects on potential carcinogenic intracellular viruses.

Exposure in the shorter UV-C (0.200 µm-0.280 µm) and the longer UV-A ranges seems less harmful to human skin. The shorter wavelengths are absorbed in the outer dead layers of the epidermis (stratum corium) and the longer wavelengths have an initial pigment-darkening effect followed by erythema if there is exposure to excessive levels.

ref: [www2.lbl.gov]