Effect vs. Power....?

[Aiki1]

Question - how powerful does a green laser have to be to feel it on the skin - and would it be the same for a red? Does the question makes sense?

 

[TigerhawkT3]

The wavelength (color) only affects visibility. If you have a 100mW blue, 100mW red, 100mW green, and 100mW IR, they'd have the same effects on targets (such as "the skin" - don't try this at home, kids). However, you'd be able to SEE the green the best, then the blue, then red, and you wouldn't be able to see the IR at all.

 

[Aiki1]

That's what I thought, thanks. So, at what level of power will a laser be felt on the skin? I'm wondering because I have what should be a 40mw red module and I don't feel it at all and I wonder if I should, i.e., if it's operating at full power....

 

[TigerhawkT3]

OUCH! Thanks a lot, buddy!

I have a 50mW green, and yes, you should DEFINITELY feel that after just a few seconds. (Distance ~3mm.) It's not exactly a lightsaber, but if it's held on the same point for a few seconds, a sharp pain occurs very suddenly.

By the way: Be careful!

 

[marshall]

That's what I thought, thanks. So, at what level of power will a laser be felt on the skin? I'm wondering because I have what should be a 40mw red module and I don't feel it at all and I wonder if I should, i.e., if it's operating at full power....

My 60mw laser could not be felt on normal skin (sometimes if the area was dark though).

Our skin is comprised of mostly clear/opaque layers though. The heat is dissapated some on the surface.

But, technically speaking, isn't it true that the colors are not all absorbed the same by our skin due to different absorption properties of the wavelengths?

For instance, 100mw 10.6m wavelength should burn when 100mw 532nm shouldn't too much on the clear skin, correct?

 

[allthatwhichis]

For instance, 100mw 10.6m wavelength should burn when 100mw 532nm shouldn't too much on the clear skin, correct?

10.6m wavelength? :huh2:

 

[wells05]

The laser's divergence and individual skin tone/pigmentation will affect the "stinging" sensation.

 

[TigerhawkT3]

10.6m wavelength is squarely in the realm of radio waves. Those go right through you, and I've never heard of a laser with that wavelength.

If your laser actually is 60mW, it does have burning capability. If, HYPOTHETICALLY, a >50mW laser were pressed to skin (yes, even white skin) and activated, there would be a sharp sting within a few seconds.

 

[IsaacHayes]

I would think a red would be less to feel, since red light passes through our skin easier than say blue. Blue would probably feel more.

I can take a 60lumen red/orange luxeon and not feel it on my skin, and my hand will pass most of the light. but a 60lumen lux3 royal blue I can feel the energy and it doesn't pass through the skin...

 

[wells05]

I would think that if a blue dot was made on any skin with a marker and then hit with a 635-650nm beam, one would feel it if the laser was strong enough. I'm not sure I would try it though.

 

[marshall]

10.6m wavelength is squarely in the realm of radio waves. Those go right through you, and I've never heard of a laser with that wavelength.

If your laser actually is 60mW, it does have burning capability. If, HYPOTHETICALLY, a >50mW laser were pressed to skin (yes, even white skin) and activated, there would be a sharp sting within a few seconds.

Hmm, isn't a CO2 laser in the area of 10.6 micron wavelength? Or 10,600nm? And, aren't these the wavelengths which will etch certain normally clear/reflective materials in the visable wavelengths? Please correct me if I'm wrong.

My 60mw was a Wicked L and assumed its output to be correct as Steve said he tested it at this (it wasn't sold back then). When you pressed it into the skin you would get a pin pricking feeling, but by shining from an inch you would feel nothing as you slightly moved about. On dark birthmarks you could feel it well.

 

[Aiki1]

Ah, ok, thanks everyone, I get the idea. No worries, I have no intention of experimenting on myself or anyone else anyway, it was just hypothetical regarding how much power my red module might be putting out.

 

[cbfull]

A very simple test that is relatively consistent is to make a very small dot on the back of your hand with a black sharpie, and briefly shine the laser onto that spot. You should feel it in less than a second if you can get it to stay still.

I wouldn't recommend doing that with anything greater than say, 50mW. It's quite possible to start your skin smoking.

A word of caution, this can sting and it is bad for your eyes to stare at the spot at this close range. Laser goggles would be wise.

 

[jkaiser3000]

burning sensation also depends on the beam's diameter, the smaller the better. Generally speaking, high power red pointers have a wider beam than green pointers

Also, red lasers do sting, but the sensation is deeper in the skin since it can go through it easier than a green laser, and more power is also required for that.

 

[TigerhawkT3]

Hmm, isn't a CO2 laser in the area of 10.6 micron wavelength? Or 10,600nm? And, aren't these the wavelengths which will etch certain normally clear/reflective materials in the visable wavelengths? Please correct me if I'm wrong.
...

I was referring to the 10.6 METER wavelength in marshall's post. 10.6 millionths of a meter is quite another matter, and would (hopefully) have been referred to as 10.6um.

 

[marshall]

I was referring to the 10.6 METER wavelength in marshall's post. 10.6 millionths of a meter is quite another matter, and would (hopefully) have been referred to as 10.6um.

Ahh, the "um", yes that would be me (mashall).

I had seen micron simply wrote as "m" after the 10.6 on net sources, my bad - should have known meter was "m".

But, besides all the mumbo jumbo, I'm sure anyone who knows CO2 lasers knew what I was talking about. Can someone comment on the 10.6um wavelength absorption properties vs those in the visable wavelengths? Isn't it true clear substances become an opaque in this area of the spectrum?

 

[jkaiser3000]

Yes, some transparent media become opaque at that wavelength, like some glasses and plastics. That's why you see people working with these lasers using transparent safety goggles. Kind of counterintuitive if you ask me :laughing:

On the other hand, some normally opaque materials become transparent at that wavelength.

 

[Athoul]

Yep transparent things are completely opaque at 10.6um (10,600nm). This is why they use co2 lasers for cutting glass and plastics etc. Just normal plastic goggles will provide 100% protection as mentioned, thus why co2 safety goggles are so cheap....about $9.99.

As to the sting that was asked about. The main thing here is the initial beam diameter leaving the aperture, not really the divergence. You won't really notice divergence effects at such a close range.

The standard green CNI high power green laser, has around a 0.4-0.5mm beam diameter leaving the aperture. On the other hand the smallest beam diamter I've seen on a high power red pointer is about 2.5mm in diameter. This is where the difference lies. Also absorbtion vs reflection is another.

Now why is there a difference?
Simply put, a red diode laser basically just includes the direct injected diode and a focusing lens. In fact there is no up collimator so all you have is a lens that focuses the beam to some degree or another. There are not other optics or lenses to adjust or correct the beam profile.

In greens the OC of the ND crystal generates a smaller beam profile, which is then passed along through an up collimator and a final focusing lens. The result is generally a smaller diameter beam with better collimation then the reds.

Ok so anyway, a smaller beam diameter means that the output energy ,photons, is being concentrated in a smaller area. Also called irradiance. So this is why you feel the prick with a green more often then with a red.

You should be able to feel a prick with a 0.5mm 532nm diameter beam, even if it's as low as about 20mW. With a red laser, if your skin is light along with the colour of blood will counter act the lasers burning or stinging ability. With a 635-670nm laser that has a 2.5mm diameter beam, you might not feel anything even if it is 100mW. If you have dark toned skin, then you may feel something though (all to do with absorbtion).

Hope this helps some

 

[Aiki1]

Interesting.... thanks. That also explains why my red laser looks better than the green when going for the lumia effect.... the red interacts better with the lenses being a little more diffuse....

 

[EGP]

Athoul, a thought just occured to me:

Would regular prescription glasses with plastic lenses for lightness, protect against the deep IR lasers ? (Or is it a specific type of clear plastic that's needed ?)

Cheers,
Erling