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Old 05-02-2015, 06:06 PM #1
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Question Mathematics of determining the amount of heat of a laser

Hello all, Iím new to the group, and to lasers in general. Iíve got a question that I havenít been able to find an answer for. It is a physics mathematics question related to lasers. It may be here somewhere, but part of the problem is I probably donít know enough about this topic to know what to search for. Iíd like to have a formula in which I can estimate the maximum theoretical amount of heat a laser would be expected to generate.

I think kinetic energy and heat are essentially the same thing, right? They might differ in how the values are represented, but I should be able to determine the heat with a simple conversion formula if I can determine the KE? Thus, my logic follows that (in a roundabout way) Heat = KE of one photon x the number of photons in a beam. Iím sure thereís more to it than that, and I could be completely wrong, but Iíd appreciate a good description of how to calculate the estimated amount of heat a laser beam should generate. Even if you just post links to stuff I can read so I can figure it out myself. I just need a push in the right direction. Iím thinking that the frequency of the beam and Planckís constant will probably be involved in the formula????


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Old 05-02-2015, 06:23 PM #2
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Default Re: Mathematics of determining the amount of heat of a laser

With a little more browsing I came across this. I think this is the answer I was looking for. I'm understanding parts of this, but if somebody can hold my hand and walk me through this process, I'd be very grateful. https://www.wyzant.com/resources/ans...s_are_produced
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Old 05-02-2015, 06:24 PM #3
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Default Re: Mathematics of determining the amount of heat of a laser

A laser beam has no temperature - there is no inherent "temperature" to a laser beam. Heat is the random motion of matterparticles (atomic or molecular particles). A laser beam itself is not made of matter but of ‘photons, which have no mass, thus a laser beam can have no temperature.
"Heat" is caused by a laser beams energy being absorbed by a material surface and turning light energy into heat energy.

Last edited by Encap; 05-02-2015 at 06:31 PM.
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Old 05-02-2015, 06:28 PM #4
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Default Re: Mathematics of determining the amount of heat of a laser

Well yeah, I should have worded my post a little better. Still, how do I determine the resulting production of heat by said absorption?
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Old 05-02-2015, 08:06 PM #5
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Default Re: Mathematics of determining the amount of heat of a laser

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Originally Posted by kmjohnson02 View Post
Well yeah, I should have worded my post a little better. Still, how do I determine the resulting production of heat by said absorption?
IS not a simple thing to determine---many factors are involved.

Maybe this will help: How to Build a Laser Death Ray: Material Response to Laser Radiation

You need to study light matter interactions .
see: http://www.princeton.edu/~spikelab/papers/book02.pdf
and
Experimental and theoretical studies of light-to-heat conversion and collective heating effects in metal nanoparticle solutions
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Old 05-02-2015, 08:08 PM #6
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Default Re: Mathematics of determining the amount of heat of a laser

Awesome, thank you for the links. I've been reading for the last few hours and have learned a lot!
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Old 05-04-2015, 12:56 PM #7
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Default Re: Mathematics of determining the amount of heat of a laser

This is not so much a question regarding lasers, as it is regarding materials.

You can know the energy of the laser beam easily, use an LPM or educated guess based on diode, current powering it, and lens in front of it.

The core of your question is answered by the absorption property of the material, at the wavelength of the laser. It simply tells you what percentage of the beam's full power is absorbed, and rest is reflected. Knowing the specific absorption of the material, though, is another story. I have no idea where to even begin looking for information like that.

Do you need this info for any specific purpose, or just curiosity?

If latter, you'll quite soon get good at estimating how well a particular laser burns any given surface, i.e. how powerful or deep scorch marks does any specific power of a beam leaves behind
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Old 05-06-2015, 10:15 PM #8
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Default Re: Mathematics of determining the amount of heat of a laser

Like the others have said, it depends on the material (how much light is reflected/absorbed). I'm not going to repeat the information the previous guys mentioned. Try instead calculating the energy of the photons.

I assume the equation for the energy of a photon is included (E=hf). Now, for the number of photons I assume (again) that you would need to know the beam diameter (and if you want to get more accurate calculations, knowing the divergence of the beam would help a lot) and the wattage (as it's basically the number of photons in a beam-in a way-the rate of energy transfer with respect to time). More mW=more photons passing through (If I'm not mistaken).

And the answer you're looking for, is it the total energy produced by the laser in a second? Because the "heat" (the energy transfer) depends on the time. More time you leave the laser on=greater energy transfer to the material

I probably haven't helped a lot, but here are my 2 cents (or 1 cent, or even less, meh)
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Old 05-07-2015, 01:37 PM #9
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Default Re: Mathematics of determining the amount of heat of a laser

Quote:
Originally Posted by Eudaimonium View Post
If latter, you'll quite soon get good at estimating how well a particular laser burns any given surface, i.e. how powerful or deep scorch marks does any specific power of a beam leaves behind
Laser focusing play an important part too. Thus more to learn how to make small or just right size spots.

Hopefully the OP did not drown in the ocean of knowledge
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