Lasers

[Brad]

Okay this is a question...

 

What is the minimum required power of a laser (in standard wavelength ~650nm) to cut through steel quickly? In addition how much power would be required to run this laser? Which kind of laser would be best? (ie HeNe, CO2, etc) I'm kind of interested in building a "poor man's laser" but as with everything "if it's worth doing it's worth overdoing.":D Thanks.

[fafalone]

To really cut through steel quickly, you'd need an extremely powerful laser with a power output of 1000W or higher. You'd want to use a CO2 laser or a COIL one, or anyone that could produce that much power. Lasers with this much power would be really hard to build without permits and alot of money, but entirely possible

[mike]

Mini-me... stop humping the lassserr.

[Radical Edward]

pumping tonic water with UV light is a good one, since the quinine will lase.

 

making a really powerful laser is rathr impractical unless you have the required tools, since there is normally a huge amount of heat generated, which disrupts the laser in a variety of ways. hence cutting lasers usually require the gas to be pumped round, often at supersonic speeds.

 

tbh, while making a laser would be fun, I wouldn't bother, you might blow it up or damage your eyesight unless you really know what you're doing

[Guest Hogslayer]

One problem with industrial cutting using lasers is plasma interaction.

 

The cutting area has to be continually "washed" with inert gas, requiring not only a laser, but a cutting chamber. And the laser has to be pulsed.

 

I have never seen anything but a small one. Pretty impracticle for cutting a large object. Plasma cutting works much better.

[Ozman]

... I can talk to this one. All the replys so far have been generally accurate, but...

 

First: Permits, etc.

 

The federal authority for laser systems (where the beam never leaves a building or other completely enclosed space) is the FDA.

Law reference is Title 10, United Staes Code, Ithink its chapter 14. It breaks down to this: unless you intend to sell it to somebody, transfer it to somebody, or use it on somebody (or their pets), the folks at FDA don't care if you build it or run it. They do care HOW you run it, and there are guidelines. If you employ others to operate the laser or to work in a situation where there is potential exposure, the FDA has specific guidelines they are more than happy to call to the attention of OSHA. Some States (Florida, Texas, and California for sure-there is a web site with links, I just can't find the URL right now) have their own regs.

 

It takes some money, but CO2 is still the most practical and cost effective as an ameteur laser project for cutting steel.

 

It takes good mirrors-make them yourself. Estimate 100 to two hundred hours to grind, figure, and test each of them. If you try to cool them with liquid, they'll need a different beginning figure.

Then pay somebody to coat them for you. And always check the results before you mount them. Scientific American used to sell a book: Ameteur Telescope Making, Book One. It has everthing you need to learn to make good mirrors for a CO2.

 

Static gases cavity design won't give you much but a hard time. Figure on a near-atmospheric pressure, and moving the gas mix quickly. Moving it accross the cavity vice along its length is a good idea.

 

Consider a TEA excitation scheme as the easiest to fabricate and one of the more difficult to love. If you don't know what any of that is, then you really need to look it up.

 

It doesn't HAVE to be a pulsed laser, but there are a couple big advantages: (1) the the material expelled (ablated) by the beam can be fully ejected from the cut area before the next pulse arrives. With a CW instead of pulsed, that ablated material forms a plume between the beam and the material, messing up the carefully calculated and meticulously crafted laser beam -to-working surface interaction.

 

(2) Pulse structure vice CW also allows the gas mix to "relax". Not in the atomic theory sense, but in a turbulent, inert fluid interacting with high energy electrical discharge sense.

 

You don't HAVE to wash the work space with inert gas, but you really, really want to do that.

 

Just a tank of CO2 won't get you there as an active medium. You also need a tank of something to mix with it. Several different mixes have been demoed. A three gas mix (you can make a primative manifold using stainless pipe and valves salvaged from a defunct restaurant someplace) is the highest efficiency. Several papers from the mid-to-late seventies have good source data.

 

There is a danger to eyesight with almost ANY laser. With High Power CO2, at 1KW, there is a slight danger of cutting off your leg, or maybe most of a finger (I have all mine). A company used to build 2kw, CW CO2's in Orlando. They tested the raw beam alignment (no focusing optics so it was over an inch across) by placing a block of 2 inch thick lexan in front of it. The burn left behind in two seconds or so exposure was nearly all the way through if the alignment was good and the flames shot out a couple feet. what was left behind was a three dimensional picture of the "mode structure" of the beam. Lots of laser safety info on the web-the best safety equipment anywhere is a clear head.

 

Now, Brad, back to your original question

 

What is the minimum required power of a laser (in standard wavelength ~650nm) to cut through steel quickly? In addition how much power would be required to run this laser? Which kind of laser would be best? (ie HeNe, CO2, etc) I'm kind of interested in building a "poor man's laser" but as with everything "if it's worth doing it's worth overdoing." Thanks.

 

 

650 nm is a "de facto" standard wavelength for things like supermarket scanners, weapon aimers, pocket pointers. It is that wavelength because it is (a) cheap to produce laser diodes in that wavelength, (b) it is visible.

 

For cutting steel, you want power (energy/time) sufficient to melt the steel, then you want a puff of inert gas to push that bit of molten steel off the work surface, and then you move the beam incrementally before the next pulse of light, regardless of what the wavelength is. CO2's most efficient spectra is 10.6 microns, thats 10,600 nm.

 

How much POWER to run it? Good question. Smart question. The efficiency of a TEA CO2 like I described here MIGHT get up to around 7 or 8 percent wall plug efficiency if the alingment and gas mix is really, really good. So don't plug it into a source that can't give it around fifteen thousand to twenty thousand watts.

 

Actually, I have built a lot more (hundreds) Nd:YAG lasers than the one CO2. Not cheap. Not a good ameteur project. But they make pretty cuts in most materials. But plasma is still better for steel. I saw a used plasma bed for sale on the web for around $7K, no PC included. You could build just the CO2laser, no moving bed, etc. for maybe $3K and a thousand hours.

 

Your call.