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Author Topic: Why do lasers produce heat as well as light?  (Read 4986 times)

Offline unstman

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Why do lasers produce heat as well as light?
« on: 22/02/2010 12:30:02 »
David asked the Naked Scientists:
   
If a photon, light, has zero mass, why is it that a laser beam can produce light and heat?

Wouldn't this prove that photons have mass as a consequence of this reaction?

What do you think?
« Last Edit: 22/02/2010 12:30:02 by _system »


 

Offline graham.d

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Why do lasers produce heat as well as light?
« Reply #1 on: 22/02/2010 14:10:33 »
Photons have zero "rest mass", but have energy that can get imparted when absorbed. The energy is in the changing electromagnetic field. However, it is a consequence of quantum mechanics that photons should be regarded as wave-particles. This has no real analogy in the larger world we are familiar with but can be shown experimentally and theoretically. So photons can be refracted and diffracted like a wave but can impart all their energy in a small area and behave like a particle. However you consider it, the energy of a photon is inversely proportional to the wavelength (which for visible light, determines its colour with violet being the most energetic and red the least). Lasers get their unusual power from the intensity they can deliver - numbers of photons per second.

Just to clarify, photons can only move at the speed of light so if they had rest mass, relativity would predict them to have infinite energy.
« Last Edit: 22/02/2010 14:12:40 by graham.d »
 

Offline lightarrow

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Why do lasers produce heat as well as light?
« Reply #2 on: 22/02/2010 15:03:46 »
David asked the Naked Scientists:   
If a photon, light, has zero mass, why is it that a laser beam can produce light and heat?
Wouldn't this prove that photons have mass as a consequence of this reaction?
"Consequence" according to which reasoning? There is no physical law which gives such a statement.
 

Offline flr

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Why do lasers produce heat as well as light?
« Reply #3 on: 27/02/2010 04:27:58 »
If a photon, light, has zero mass, why is it that a laser beam can produce light and heat? Wouldn't this prove that photons have mass as a consequence of this reaction?

The energy momentum relation is:
    E2 = m2 c4 + p2 c2
where m is the rest mass, p is the momentum, c is the speed of light.

This relation indicate that "particles" with no rest mass (like photons) can still have energy:
  E=pc

It is possible that this energy dissipate as heat.
 

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Why do lasers produce heat as well as light?
« Reply #3 on: 27/02/2010 04:27:58 »

 

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