# what makes the laser burn



## Cdawg (Apr 15, 2007)

if anybody saq my old post about me modding a leadlight, with the pot mod to the point that it burns skin.

but i wanna know what causes it to burn.

does like the laser frequency heat the particles in the air causin u to burn. or is the laser beam itself hot....idk


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## picrthis (Apr 15, 2007)

Cdawg said:


> if anybody saq my old post about me modding a leadlight, with the pot mod to the point that it burns skin.
> 
> but i wanna know what causes it to burn.
> 
> does like the laser frequency heat the particles in the air causin u to burn. or is the laser beam itself hot....idk



Radiation.


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## FNinjaP90 (Apr 15, 2007)

The laser is a device that transmits energy from its source to the target through radiation, and in this form green light. That transfered energy heats up an object depending on how well it absorbs that radiation. 5mW green lasers just don't put out enough power (energy per second) to produce a noticeable heat buildup.


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## Corona (Apr 16, 2007)

It's about energy density (concentration) as well

The energy from the Sun hitting the earth is about 0.14 watts per square centimeter. Won't even burn a hole in a plastic trash bag at that concentration...

But if you take a 10cm diameter magnifying glass and _collect_ some sunlight... 

10cm diameter = approx 80 square cm area; so 80 * 0.14 = 11.2 watts collected (assuming "perfect" optics)

now focus that energy down to a 1mm (round) spot, you will have increased the power density to 14.27 watts per square millimeter, or 1,427 watts per square centimeter. And now you can easily melt plastic, ants, metal, or your cornea with it. 

By comparison, the energy from a 100mW laser, focussed to a 1mm spot, is approx. 12.7 watts per square centimeter.

1mm diameter spot = 0.785 square mm


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## Aseras (Apr 16, 2007)

it's irridiance. the more photons that hit the more energy that just be absorbed or reflected. You can either use more photons ( more power ) or concentrate them to smaller area ( focus )

Think of water on tissue paper. a slow drop will be scattered/absorbed by the paper but do no damage. more water might cause it to break or saturate. a small stream/jet of water at higher pressure will pierce right through it.

now with lasers that are very high power ( like 100+watts ) in a small beam, you can actually ionize ( cook ) the air and the nitrogen in the air itself begins to laze a bright blue.

it does all boil down to power and it's area of affect. it's why a 30mw with a tiny dot can pop a ballon cut etc, but a 100 mw with poor focus can't do anything.


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## Cdawg (Apr 17, 2007)

could constantly heating/burning yoru arm to check battery power give you ckin cancer


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## Timson (Apr 17, 2007)

Cdawg said:


> could constantly heating/burning yoru arm to check battery power give you ckin cancer



What doesn't cause cancer now-a-days :scowl: 

I wouldn't make a habbit of it... If you're feeling 'burning' you're damaging skin tissue - A bit like sun burn.


Tim.


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## luvlasers (Apr 18, 2007)

Naahhhh laser beam is not more likely to give you cancer than a torch light. 

Go back to why UV light gives a greater incidence of cancer. Cos the UV light properties cause mutations within cells of your skin at the molecular level.

Lasers are just concencrated (don't shoot me for this horrible generalization) light with in the visible spectrum.


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## SenKat (Apr 19, 2007)

Well - the pain felt when you get burnt, is the brains' way of saying, "Don't do that again !" My brain has been telling me for over two years that I am stupid for falling off my roof !


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## Gunner12 (Apr 20, 2007)

Shining a Laser on your arm probably doesn't increase you chances of getting skin cancer by much. Your chances of getting skin cancer increases much more with a sunburn.

Why it burns, another explanation:
The radiation from the laser transmits some of it's energy to you skin, the paper or whatever you are trying to burn. Some of this energy is turned into heat (darker = more absorption), and if the heat reaches a certain point, the substance will start to smoke. If raised to an even higher temperature the substance will ignite and catch fire.

In theory, if you focus a key-chain laser pointer enough, it will have enough burning power to cut metal.

Of course, more power in a set beam diameter also means a quicker time to ignition.


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## 2xTrinity (Apr 20, 2007)

> Go back to why UV light gives a greater incidence of cancer. Cos the UV light properties cause mutations within cells of your skin at the molecular level.
> 
> Lasers are just concencrated (don't shoot me for this horrible generalization) light with in the visible spectrum.


Yep. And here's a simplified reason why UV in particular causes problems:

light essentially transmits energy in photons. Let's say you have lasers of identical power output, one of them is UV, and the other is visible. Both will be transmitting the same total amount of energy, buy in the case of the visible light, it will be sending it as a whole bunch of "weak" photons that don't by themselves have very much energy. In the UV beam however, there will be fewer photons, but they will be much more energetic -- even though the total energy is the same, the collisions from the higher-energy UV photons will do more damage, as each one has enough energy to mess up the DNA inside a skin cell (for example).

Both lasers however if you were to shine them at a black piece of paper would heat up the paper by the same amount. Burning your skin (with heat, not UV) isn't going to cause cancer, though I wouldn't recommend making a habit of it.


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