Guys, different types of laser produce different wavelengths, and you need to select the right wavelength for the material in question, eg a wavelength that is absorbed.
Invisible IR from a CO2 laser is ideal for cutting / marking acrylic, marking glass, cutting / marking wood, leather, etc etc...
Here in the UK you can buy *********e chinese aircooled CO2 lasers for around 250 quid for 25 watts, just add a neon sign transformer and some fans and you're good to go, for a couple of thousand hours.
Pukka sealed for life and lasts for 5k 10k CO2 hours laser cost more, as do water cooled.
Coherent and Synrad both make visible spectrum diode lasers in the multi watt range, (as well as CO2) not so good at cutting transparent materials or metals... quite expensive because you end up needing a quality PSU that can deliver 100 amperes at 2.0 volts, exactly for even a moderately powered beam...
CO2 is a lot more versatile, you can cut metal with it, just a question of power.
As a rule of thumb, you get about 2 watts of power per inch of tube, think on this if planning on mounting the tube in the Z axis, if not, if planning on using flying optics, good luck to you on the precision front.... think about it.
A 25 watt CO2 laser will slowly cut clean through 10 mm acrylic, a 100 watt will cut eighth inch steel plate.
CO2 laser basically operate at RF, so you can switch them on and off very, very, very fast, which can be useful.
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Now, everyone talks about eye safety, and this is true, even a 1 watt laser focused by the eye lens on the retina will permanently blind you before your brain even begins the blink reaction, and thats a visible laser, IR is even worse, except IR flashback can be very easy prevented by using an IR opaque medium, like acrylic or pilkington glass, this is how greenhouses work after all
HOWEVER
Permanent blindness is not the issue.
I emailed tweakie about this, a laser essentially creates a high energy plasma cloud of chemical elements from the substance being lasered, and all sorts of rubbers and plastics and other materials start giving off clouds of extremely toxic and / or carcinogenic compounds like benzine, phosgene, arsenic, chlorine etc etc etc...
Laser cut steel creates clouds of micron sized rust
Laser cut stainless steel creates clouds of very nasty heavy metals like chromium etc that once absorbed the body can never rid itself of...
As I said to tweakie it would probably be healthier to hand my small son a lit cigar than to let him be in the same room as a cutting or engraving laser, even if he was wearing a welding mask...
CO2 lasers are a lot like gas axes, they have a jet of gas (often just dry clean air) shooting out the same nozzle as the beam, and the gas jet is what really does the cutting, the laser just melts.
Essentially the difference between a 25 watt CO2 laser and a 100 watt CO2 laser is that any job the 25 watt one can do, the 100 watt can do at 4 times the feed. However, but there is a lower limit for each material and job, and that limit is the ability to punch through fast enough to have minimal deflection and to move fast enough to have minimal heat going anywhere except the desired spot.
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DO NOT BUY 150 mW laser diodes for big bucks, every single old CD burner has one in it with a lens, for free... DVD burners nearer 200 mW.
a suitable hole bored longwise in a CPU heatsink and fan is good for cooling, and long life on diodes is good cooling, good power (within limits), soft start and stop
Forget visible light diode lasers unless you want to run a light show, invisible IR is where it is at for delivered energy, but requires slightly special optics, not just ordinary glass lenses.
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If you're serious about it a 25 watt CO2 tube, neon sign transformer and tube cooling is dead simple, and actually works out a lot cheaper per watt than a 150/250 mW diode bought new, plus PSU, etc, and optics are affordable, and a clean air supply for the jet, just watch out for the 22kvolts and the instant blindness or instant 3rd degree burns, but you be able to cut most organics and plastics up to 10mm thick slowly, and engrave most plastics, glass, and organics and even metal (after pre treating) quite fast indeed.
HTH etc
cheers