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I conducted an experiment today. I heated a laser beam by shining it through a piece of 1/2 inch copper pipe about 10 inches long. I then heated the pipe until most of it was glowing red. The beam exited the pipe and traveled to a solar cell where I measured its voltage. The voltage and the beam's image were not affected by the heated pipe. There were similar readings for both hot and room temperature. My question is has anyone tried this with more heat and with different results? I know light can heat things, but can light be heated. The purpose of the experiment was simply to gain greater understanding as to the nature of light. enter image description here

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    $\begingroup$ Presumably, if you had looked closely, you might have seen small deviations in the path of the laser beam, but those would come from the heating of the air inside and around the entrance/exit of the pipe. But, no, the photons just don't care. $\endgroup$ – Jon Custer Feb 15 '17 at 22:00
  • $\begingroup$ -1. Your experiment showed that heating the pipe did not affect the laser beam - the beam did not gain or lose energy, and the size of the spot did not change. So your experiment answered your question. $\endgroup$ – sammy gerbil Feb 15 '17 at 23:54
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    $\begingroup$ Sammy, Sammy, you gave me a -1 and you didn't even read my question. I know you have it in you to reconsider. What would happen if a beam passed through a 2,000 degree, area? What about 10,000 degrees? My question was what happens at temps beyond mine. Maybe know one has tried. That's why I asked. $\endgroup$ – Lambda Feb 16 '17 at 1:03
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    $\begingroup$ I'll give you the +1 back. I, for one, appreciate someone who has a question and chooses to experiment on it first, and only then queries the community to understand the greater model within which this experimental data fits. I prefer that greatly over asking the internet for truths and then blindly accepting what they say. $\endgroup$ – Cort Ammon - Reinstate Monica Feb 16 '17 at 2:07
  • $\begingroup$ @Lambda Well, questions like "Nothing happened in my experiment. Could something happen in a different experiment?" are kind of lame. Of course it's possible to modify an experiment to get something to happen. $\endgroup$ – DepressedDaniel Feb 16 '17 at 3:09
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In principle, the scattering of photons off the gas molecules of the flame can carry away heat in some circumstances (this is for example used in laser cooling). If the transition frequencies of the atoms is close to the laser frequency, photons can carry away momentum.

But your laser is such an open system that any scattering of photons off the hot gas molecules of the flame probably just dissipates the heat in all directions. It makes no sense then, to talk about an ensemble of photons with a temperature. If you were to collect some photons, say by shining them into a high-finesse cavity constructed from mirrors, it could perhaps be possible.

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The notion of temperature can be applied to a photon gas, but I believe that laser is a very cool system even at very high energy density.

The pictured experiment is naive, but in a clever way.

I presume the idea is that you warm the beam but putting it near a hot thing (the heated tube), yes? That certainly works with material objects, after all.

It works for material bodies because of radiative transfer, but light is characterized by linear superposition which means that it passes through other light without either beam incurring a lasting effect from the encounter.1

So you're not heating the beam that way.

As noted in the comments there will be some interaction with the hot atmosphere inside the tube, but given the scale of the experiment pictured it will be modest.


1 Light can exhibit non-linear interaction is some fairly special materials, or in many more materials at high intensity, and even without a material medium at very high energy or extreme intensities, but none of those condition obtain here.

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    $\begingroup$ Yes, the tube was my way of heating the beam without the flame itself becoming a factor. When the flame was placed directly in the beam a small change to the laser dot appeared. I assumed it was just the opaque qualities of the blue flame scattering the laser, not the heat. $\endgroup$ – Lambda Feb 16 '17 at 1:21

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