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Which laser is most powerful?

  1. Oct 23, 2009 #1
    I suppose this thread should belong to a seperate 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.
     
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  3. Oct 23, 2009 #2

    Vanadium 50

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    Watts are a unit of power. So 500 mW is 500 mW - they have equal power.
     
  4. Oct 23, 2009 #3
    Of course, the blue laser is most powerful in all respects out of the three.
     
  5. Oct 23, 2009 #4

    Vanadium 50

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    How can that be? Are not watts watts?
     
  6. Oct 23, 2009 #5
    Of course not. We speak of spectral power. The blue light is more penetrating, more dammaging, more agressive, if you like.
     
  7. Oct 23, 2009 #6
    Last edited by a moderator: Apr 24, 2017
  8. Oct 23, 2009 #7
    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
    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.
     
    Last edited: Oct 23, 2009
  9. Oct 23, 2009 #8

    Vanadium 50

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    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.
     
  10. Oct 23, 2009 #9
    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 - infra-red or X ray?

    In non-equilibrium state the absorption power is proportional to T24-T14. Obviously this difference is higher for the blue colour.
     
    Last edited: Oct 23, 2009
  11. Oct 23, 2009 #10

    Redbelly98

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    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.

    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.

    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.
     
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