Which Color Laser Burns Paper Fastest at Equal Wattage?

[univeruser]

I suppose this thread should belong to a separate group called Light - that is, I suppose this should be where Quantum Physics should be.

As for the question, I'd gladly explain that it is of a laser. I wanted to get a laser at Wicked Lasers (I know, with the LaserShades, of course), but here I'm stuck in a tight spot. Look, we have a red, green, and blue laser. The wattage we'll take to be around 500 mW for each laser. Now, if this is so, which one's beam is most powerful, by means of the heat generated on contact with a object? Red, green, or blue?

I'd also like to know why this is so, and if a difference in the wavelength causes it to have more or less burning power on say, for instance a piece of paper.

 

[Vanadium 50]

Watts are a unit of power. So 500 mW is 500 mW - they have equal power.

 

[Bob_for_short]

Of course, the blue laser is most powerful in all respects out of the three.

 

[Vanadium 50]

How can that be? Are not watts watts?

 

[Bob_for_short]

How can that be? Are not watts watts?

Of course not. We speak of spectral power. The blue light is more penetrating, more dammaging, more aggressive, if you like.

 

[Count Iblis]

A green laser beam is going to look brighter because our eyes are more sensitive to green light. Not sure though why they used a green laser http://blogs.techrepublic.com.com/geekend/?p=277"

 

[ully]

Of course not. We speak of spectral power. The blue light is more penetrating, more dammaging, more aggressive, if you like.

Remember that the energy levels per photon are vastly different at different colors, the red might shoot twice as many photons as green but they hit half as hard- and as such may not be enough to have the desired effect of

by means of the heat generated on contact with a object? Red, green, or blue?

Many solid state visible light lasers start as infra red, but progressively pass through lazing mediums that add the photons energy together and emit a new more powerful level of photon, and this process continues to the desired color. And Bob is also certainly correct that blue is the most aggressive of the three.

Do not scoff at how extremely damaging to the eyes lasers can be- particularly with green and blue if you are close enough to the target (based on reflectivity properties) you can get eye damage (not just looking into the emission) even a paltry 100mw red laser can do far more damage then staring at the sun across a very small area, so you will not notice how much damage you accrue until it is too late. A more powerful one can instantly blind you.

 

[Vanadium 50]

Of course not. We speak of spectral power. The blue light is more penetrating, more dammaging, more aggressive, if you like.

Aggressive? Awfully anthropomorphic, no?

Blue light carries more energy per photon than red light, to be sure. But for equal power, there are fewer photons per second of blue light than red light.

Asking which has more power, a watt of red light or a watt of blue light is like asking which weighs more: a pound of feathers or a pound of rocks. A pound is a pound. And a watt is a watt.

 

[Bob_for_short]

...which weighs more: a pound of feathers or a pound of rocks. A pound is a pound. And a watt is a watt.

If a pound is a measure of mass, then a pound of feathers weights less than a pound of rocks, because the weight is (mg - Archimedes force). For rocks the Archimedes force is smaller.

About radiation: which is better absorbed - infrared or X ray?

In non-equilibrium state the absorption power is proportional to T₂⁴-T₁⁴. Obviously this difference is higher for the blue colour.

 

[Redbelly98]

I'm firmly with the "500 mW = 500 mW" camp here. The question was about the ability to burn through a piece of paper, presumably white paper. I.e., pretty much equal absorptivity and reflectivity across the visible spectrum.

To burn, the paper must absorb a certain amount of energy per unit area. We have equal powers, equal absorption, and presumably the laser beams have equal cross sectional areas. So the paper gets to the same temperature in the same amount of time for any of the visible colors.

A green laser beam is going to look brighter because our eyes are more sensitive to green light.

True. But the OP's question was not about which appears brighter, it was which can burn paper faster. The fact that our eyes are more sensitive to green is irrelevant. A white sheet of paper is equally sensitive to red, green, and blue.

Of course not. We speak of spectral power. The blue light is more penetrating, more dammaging, more aggressive, if you like.

If I read the OP's question correctly, it's not an issue of causing damage by photoabsorption. It's a simple matter of heating up paper to the point where it catches fire or starts charring.