Laser Energy Reflection: Understanding Photon Build-Up in a Vacuum

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Discussion Overview

The discussion revolves around the behavior of laser energy and photon dynamics in a vacuum when reflected between two mirrors. Participants explore whether photons build up indefinitely and the implications of energy loss in this system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if photons continuously build up when a laser beam bounces between two mirrors in a vacuum, asking where the energy goes if it does not.
  • Another participant speculates that energy may be lost as heat through infrared waves.
  • Some participants argue that it is impossible to arrange finite mirrors to allow indefinite bouncing of a laser beam, noting that real mirrors absorb some energy with each bounce, converting it to heat.
  • It is suggested that the energy converted to heat in the mirrors must equal the energy coming from the laser; otherwise, there would be excess energy that needs to be accounted for.
  • One participant posits that while most energy remains as photons bouncing between the mirrors, some energy is lost to heat with each cycle, leading to a finite system unless a constant energy supply is introduced.
  • Concerns are raised about the imperfections of mirrors, which would result in additional photon loss, further emphasizing the finite nature of the system.

Areas of Agreement / Disagreement

Participants generally agree that finite mirrors cannot support indefinite photon bouncing and that energy loss occurs, but there is no consensus on the specifics of energy dynamics or the implications of these losses.

Contextual Notes

Participants acknowledge the limitations of real mirrors and the assumptions regarding their properties, as well as the hypothetical nature of maintaining a constant energy supply.

Gmanme
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Question,


If in a vacuum, I have a laser pointing into a mirrior which bounces between two mirriors on the same spot, do the photons / laser energy continuously build up? If not whare does it go?
 
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I don't know for sure, but I imagine it's lost as heat via infrared waves.
 
You can't arrange a pair of (finite) mirrors so that you can fire a beam in and have it bounce back between them indefinitely.
If you could then with real mirrors a small amount is absorbed on each bounce and so the energy would gradually be converted to heat in the mirror.

Some types of laser are made from a pair of mirrors. Light bounces between them traveling back and forth through a laser medium, but you need to feed energy into the laser medium material to make new photons.
One of the mirrors is usually semitransparent to let the laser light out.
 
mgb_phys said:
You can't arrange a pair of (finite) mirrors so that you can fire a beam in and have it bounce back between them indefinitely.
If you could then with real mirrors a small amount is absorbed on each bounce and so the energy would gradually be converted to heat in the mirror.


The amount of energy converted into heat in the mirrior would have to equal to the amount of energy coming from the laser. If not, the there's excess energy that has to go somewhere.
 
Gmanme said:
The amount of energy converted into heat in the mirrior would have to equal to the amount of energy coming from the laser. If not, the there's excess energy that has to go somewhere.

Most of the energy would remain as photons bouncing between the mirrors, but it would loose a bit of energy every bounce-cycle to heat so the system would run out eventually. In fact, it would run out exactly when you lost 100% of the energy you put in as heat. Also, unless the mirror is absolutely flawless (which I bet is impossible), you'll loose some photons that way too as they aren't redirected perfectly to the other mirror. So it's finite, unless you had a constant supply of energy to keep producing photons, but then we're talking just hypotheticals at that point. Also, to reiterate, the other guy said you can't set up finite mirrors like that anyway and he has a lot of posts so I bet he's right.
 

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