Eye protection, Beam alignment and focusing beams

[Ya-Nvr-No]

Can we get a thread started about Eye Glasses and what people are using and why. Lots of different wave lengths but I am at a loss as to what wave length glasses to choose and for what reason I would use them. (other than when I open the cover of course)

And how beam alignment is done safely. I have been using a piece of paper in front of each mirror to check for centering. Seems like there must be a safer way.

I did manage to get the DSP mounted in the SOLO and now with a flip of a few switches I can use either driver board. I will post some photos of my unit if I can get some interest in this thread.

Thanks
Ya-Nvr-No

http://www.yanvrno.com

Edited 7-9-2011:
Couple of sites I found some info about CO2 lasers:
http://www.rp-photonics.com/co2_lasers.html
http://www.rp-photonics.com/eye_safe_lasers.html

[baccus61]

Hi Ya-Nvr-No,
I use stock standard off the shelf poly carbonate safety glasses for my CO2 laser
.
One way to test if your glasses are ok for use is to place a piece of tobacco paper (rice paper) under the lens and focus your laser for the paper then turn on the laser for a quick burst to see if it burns a hole into the paper. (while your NOT wearing them). If it does then it's probably not very suitable for protection.

A lot of people think the beam when reflected off a surface is still focused, but, if the beam has travelled through a lens then the beam will be dispersed at an inverse proportional amount. ( it gets weaker by the square of the distance). so by the time it hits your body parts it will have lost a lot of it's power and you might just feel a warm sensation where the beam hits you.

BUT, if you place any of your body parts into the path of the beam before it has been focused then you will be in for a whole world of hurt. Been there done that when I first set up my laser and still have the scar to prove it. This shouldn't happen with the Lightobject DSP as it won't turn on unless you tell it to. My old set up used a BOB and Linkmotion Tm and when Windows first starts up it tests all the parallel port pins by turning them on. Really handy when your reaching for a piece of card stock to cut and have your forearm in the way of the full 30 watt beam. Thank God I didn't have my 100 watt laser set up then

When you align your mirrors use a piece of thick card stock about 2mm thick or a thin piece of wood. Paper will leave a residue on the mirror that you will need to get off later and if you are using the gold mirrors then you need to be really careful not to scratch them as Gold is very soft, as you probably already know.
If you have Gold mirrors as I suspect 99% of the people out there do then you need to get a piece of lens cleaning cloth and wet it and drape it across the mirror and then very slowly drag it off the mirror without applying any vertical pressure to it. Do this again with another clean spot on the cloth until the surface is clean. It may take a while. If you can't get a spot clean then you will need to apply a bit of pressure but only do this if you absolutely need to. If you use a cotton wool bud or Q-Tip then you WILL scratch the mirror surface and it won't be long before your power drops off due to the beam being dispersed by all the minute scratches on it's surface. You might have seen some of the people doing this in the laser set up videos. THIS IS WRONG!!!!!

I used Aluminium first surface mirrors from a photocopier with my first laser build and I used to use Q-Tips on them and sometimes had to rub really hard to get the gunk off them and they are still near new with very little scratching on them. The Al surface is WAY more durable than the gold mirrors are.

Use care with the ZNSe lenses as they as also soft AND brittle and are very easily broken. I dropped one from about 4 inches onto my table and shattered it to pieces. be careful of them.
Also treat them like the gold mirrors as they have an anti reflective coating on them that can be harmed if they are abused too much.

When aligning the beam start at the output and the first mirror in front of the laser and give a short pulse at a low power to see where the burn is on your card. Don't hold it directly on the mirror surface as you might get smoke resudue on the mirror surface which is very hard to remove. get the beam close to center then work your way around the mirrors until they are all in alignment. It takes a bit of time but isn't hard. If you are worried your fingers will get in the way then fold the card so that it hangs from the top of the mirror assembly and across the face of the mirror then you can close the lid if you really want to but you will find that very tiresome very soon.

Above all, just be aware of where the beam path is and keep your body bits out of harms way.

From the Epilog site. I hope they don't mind.

Quote
"What are the different uses for YAG and CO2 lasers?

YAG lasers and CO2 lasers react very differently on different materials because of the differing wavelengths of the laser beams. The wavelength of a YAG laser (1.064 microns) is exactly ten times smaller than the CO2 wavelength of 10.64 microns, which makes it ideally suited for absorption in most metals, but this small wavelength inhibits its ability to be absorbed by many other materials (wood, acrylic, plastics, fabrics, etc.)

A CO2 laser beam is not easily absorbed by metal, but can easily be absorbed by many organic materials such as wood, acrylic, rubber, etc, while it tends to reflect off of most metal surfaces. It's the different wavelengths of the two beams that are mainly responsible for the different types of materials that they will react with. There are a number of other differences between the two lasers; thermal efficiency, heat transfer, minimum and maximum power output, etc. and these characteristics all have an affect on the materials that the beams react with. "
UnQuote

[Ya-Nvr-No]

That was a great writeup, thanks for the info and tips. Is the beam safe to look at when cutting? I assumed it was like welding, you would get arc flash burn even looking at it without protection. Or is the protection just for stray or reflected beam safety? Still a little confused by how to create a safe site for all to view. I visit places that have CO2 units and I see no one wearing anything special around the units. Why the special glasses section that are for sale then? Is this just for setups when the door is open?

I too found the mirrored beam a little warm to the back of the index finger. Lucky it burnt no flesh. TOO Friggen close, I like my skin raw not cooked.

So that leads me to a question about tube placement. Can you direct the beam straight down into the focusing lens and not use the mirrors? I'd wondered about mounting the tube vertical on my Z axis slide and either directing it through one mirror or directly into the focusing head with lens (making my own head) I'm sure I could not do it for a long tube but a 40 watt or less seems short enough to mount that way safely.

And is an exposed tube safe to look at without UV protection glasses when it is energized?

Thanks

[baccus61]

Class 4 lasers are actually prohibited for general viewing in a public place without propper shielding for the beam so the lid must be closed or a partition put in place. Those guys would not be operating in accordance with the regulations if the lid is up when working.

The special glasses would be used if the door is open.

The beam is very bright where it is cutting so try not to look at it for too long. I usually place myself in a position where the spot is obscured from view by the lens assembly air atachment but I can still see where the laser is cutting but not the actual spot where it is cutting (if that makes sense)

You can certainly place the tube directly on top of the lens assembly but don't expect to do any real fast movements as the tube is relatively heavy and the water tube inside probably wouldn't like to see fast accelerations either. It has been done but you are way better off using mirrors so the laser head is light and you can engrave a whole lot faster.

Looking at the side of the laser is fine, as far as I know, without any special glasses while it is working. Thge ionisation of the gasses is very dull.

Rich.

[Ya-Nvr-No]

Thanks Again Rich
That clears up a lot of my safety questions,

I feel assured my due diligence has and will save me from dangerous conditions.