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The Energy of laser

  1. Nov 13, 2007 #1
    Does the energy of laser depend on the wavelength of it?

    Or the energy of laser depend on the number(flux) of the photon?

    Which is more harmful? The light with short wavelength or with more photon?

  2. jcsd
  3. Nov 13, 2007 #2


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    The power is the energy (depends on the wavelength) * the number of photons /second.
    Generally shorter wavelengths ( more energy / photon ) are more harmful.
  4. Nov 13, 2007 #3
    Wavelength combined with photon flux is sufficient (but usually not practical/convenient) to determine the power of a laser.

    For a given amount of power, short wavelength is more harmful (as such photons will impart enough energy to break something whereas the innumerable photons comprising almost-static fields will evenly distribute their energy over any target).
  5. Nov 14, 2007 #4


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    Different wavelengths have different hazards. A UV laser will damage the cornea, while a visible light laser will get the retina. It is not clear to me which is worse.

    Of course any laser with sufficient power will cause burns. I have brushed a 12W UV beam with a gloved finger, it is hot....FAST!
  6. Nov 14, 2007 #5


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    Yes, but in broad terms a Watt of X-ray laser will do more harm to most materials than a Watt of RF transmitter.
  7. Nov 14, 2007 #6
    I think a sunburnt cornea is preferable to any retina damage, so I guess particular systems can have greatly heightened vulnerability to specific (finite) frequencies.
  8. Nov 14, 2007 #7


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    The general idea, I believe, is don't look at the damned things regardless of their frequencies. Even a stupid little $1.50 laser pointer can cause serious eye damage, as can the scanning head from a DVD player. However unlikely it might be, the possibility is always there.
    Generally speaking, though, as the frog pointed out, higher frequencies at a given power level tend to have more destructive effects.
  9. Nov 14, 2007 #8

    Claude Bile

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    Firstly, let us clarify what is meant by the energy of a laser. Usually we speak of laser power, but for pulsed laser systems, the energy per pulse is often quoted. Neither of these parameters depend on laser wavelength. Laser power usually depends on the pumping regime (the more energy you pump into the cavity, the more power you get at the output), details of the laser cavity (the reflectivity of the output coupler for example) and the gain medium itself.

    Laser power, photon wavelength and photon flux share a simple relationship, and given two, one can easily calculate the other, but the power of the laser does not intrinsically depend on these factors.

    Wavelengths that are transmitted by the cornea and reach the retina are the most dangerous in terms of eye safety, this includes the visible spectrum and a little bit beyond. Wavelengths that are transmitted by the cornea and do not fall within the visible spectrum (UV in particular) are extra-dangerous, because they don't trigger our blink reflex, and have the added danger of being invisible.

    Shorter wavelengths (UV and shorter) can contribute to skin damage over a long period of exposure to the specularly reflected beam and can lead to cancer in the worst case scenario.

    Of course, in all of these cases, the higher the laser power, the greater the risk. Pulsed lasers are especially dangerous as they compress the laser energy into small packets and as a result, the peak power of a pulsed laser can be some 1000 times greater than its average power. Lasers with extremely short pulses (< 1 ps) have the added risk factor of bypassing eye safety through the generation of higher-order harmonics.

    Last edited: Nov 14, 2007
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