Beam reflection WARNING !

[Dave Johnson29]

Hi All,

Well, I have some serious forelock tugging and bowing and scraping to do. I got it wrong for brushed stainless steel. I decided to start a new thread as reflection is real with some materials.

As you can see from the new pics, brushed stainless steel does indeed reflect so be careful.

Obviously the rate of thermal conductivity of stainless is not great enough to absorb all of the energy and some is reflected.

It is obviously a lower amount of energy as you can see from the small hole in the pics, it barely charred the edges of the paper. But reflected energy, there is and enough to instantly burn a hole in the paper.

For the second pic, I removed the stainless and brought the focus up to burn the paper at low power and high speed and moved the circle off to the side a bit. I wanted to get a comparison between the diameters of the actual hole traced on to the stainless and the one burned by reflection. As you can see there is not much divergence.

The final test was to tape some paper to the underside of the glass in the lid. This produced a very faint scorch mark for the first pass. I did 5 more passes and third pic shows the pattern emerging. The beam is diffusing probably from the surface of the brushed stainless steel.

The interesting thing is the beam is not diverging much. The burn size is about double the actual circle size traced on to the stainless. That burn on the paper taped to the lid was made about 10" from the stainless surface.

With high thermal conductivity materials it seems reflection is not so much an issue, but low thermal conductivity, take GREAT care. The glass on the lid did get a little warm and I suspect that the scorch would have been a nasty burn on skin even on a single pass.

[Darren Null]

Told you so. DOOOM! I said. BEWAAAAAARRRREEE the reflections I said.

Seriously, thanks for doing the experiment and posting the results- very informative and much more scientific than the guy who melted his lid. For the record, I think it's thermal conductivity + shinyness. I had some cardboard covered with shiny metallic plastic that I was burning some xmas boxes out of and I tried it shiny-side-up. Very briefly. I couldn't get through it from the back either. Should have learned from that, I suppose, but you have to try these things.

[Scott Shepherd]

TOLD YOU SO TOOOOOOO!!!!!!!!!!!!!!!!!!!!!!!!!!

Free drinks at the bar for Darren and me tonight! WoooHoooo!

Take that Mythbusters

Okay, enough gloating for now. Did we mention we told you so yet?


Well, we told you so!

[Dave Johnson29]

TOLD YOU SO TOOOOOOO!!!!!!!!!!!!!!!!!!!!!!!!!!

You guys,

I just got back from walking the dog and while on the walk I thought, "damn, I should have put 'let the told-ya-sos' begin," in that last posting

Ahhh, hindsight.

And hey, the Mythbusters don't bust everything either.

Ahhh well, the beer is cold and my dog loves me.

[Scott Shepherd]

my dog loves me.

He doesn't have any say so in it. You won't give him the keys to the truck

It's not often we get to poke fun at you and have a laugh, so I'm glad it worked out that way

I'm liking that cold beer sound.....it's 8:00 here and quiting time, so I'll just tell them "put this on Dave's tab" tonight!

You know, if your Mom was around, she'd have told you not to do it, you'd put your eye out

[Dave Johnson29]

Told you so. DOOOM! I said. BEWAAAAAARRRREEE the reflections I said.

Do not look into laser with remaining good eye. yeah, yeah, I know.

It really surprised me how little divergence there is in that 10" of travel though.

I am sure a shiny stainless surface would be even worse or better whichever way you look at it. It would behave much like a front surface mirror. The fine brushed stainless I used was food grade and had protective film on both sides so the surface was pretty pristine and shiny-ish.

Suffice to say I will be a little more cautious now. Although I do think I was pretty safe holding the footballs.

[Jack Burton]

OK I'LL eat my words too!

Cool result! Thanks!

[Russ Shoe]

yep its true....in my short experience of lasering, was marking a SS flask with thermark.....and noticed a small flame next to my lens...must have bounced back to the plastic and started it a blaze...caught it fast enough though.......yikes!!!

[Dave Johnson29]

He doesn't have any say so in it. You won't give him the keys to the truck

Ha! I know he loves me because when I open the front gate, he is the only one in the truck, keys in it and engine running.

I have noticed he does sit in the driver's seat when I am opening the gate, maybe he is getting the feel of things and one day will be gone as soon as the gate is opened. Maybe I had better start shutting the truck off and taking the keys, before getting out.

Time for beer number two. Put yours and Darren's on my tab, you can trust me.

[Darren Null]

I thought, "damn, I should have put 'let the told-ya-sos' begin," in that last posting

We got you covered there.

Suffice to say I will be a little more cautious now.

Then it's all worth it.

Although I do think I was pretty safe holding the footballs.

It's hard-to-predict invisible stuff that can make you blind. I shall be maintaining my position over here behind the sandbags.

OK I'LL eat my words too!

Told you so as well. BEEWAAAAAARRRREEEE the vibes of March, I said. Signs and portents, I said.

That's me gloated out. I shall allow myself 15 minutes of insufferable smugness, then it's back to business......

[Paul Brinkmeyer]

This has been an eye opener. I would have never guessed.

Now who's going to try to hit the mirror left on the moon by NASA?

[Russ Shoe]

Oh, by the way, I was marking the inside of the flask, was curved in, (testing) thats when the plastic around the lens got all melty. On the outside of the flask, didnt seem to do anything, and of course I watched it like a hawk after that! Didnt damage anything that I use, just one of the slots for a different lens, which I dont have.


ya just never know

[Martin Boekers]

OK, now ya got me thinking.

Maybe Dan can help with this.

Is a CO2 laser Infra red?

If so would you be able to see the beam with standard night vision googles?

If I had a set I'd try it.

Someone has to have a set and can try this for us. If it works that would be very interesting to watch the beam in action!


Marty

[Darren Null]

If wikipedia is to be believed and I've got all my nanos and microns in the right place, night vision goggles usually inhabit the 'near-infrared' band which is 0.75-1.4µm; whereas CO2 lasers run at 10.6µm which is 'long wavelength infrared'.

You'd be able to see the beam with a thermal imaging camera, but those look a bit pricey.

[Rodne Gold]

Not surprising you would get a "hot" reflection considering the mirrors on your laser are gold plated polished steel.