Light Trap. Would this work?

[arkain101]

This is something that I have wondered about quite often. What are ways you can trap light and if you can, can you have it doing work while it is trapped?

 

If you take a concave mirror:

 

 

and allow the sun's rays to shine onto the mirror the focus point can be hot enough to boil water or even burn objects. Now the question is. Is it possible to use two mirrors facing eachother so that the light will not escape once it gets in. Then allow the suns light to make its way into the mirrors "closed system" so that it fills the space between the mirrors with a huge amount of light energy?

 

The purpose of such a device would be to capture large amounts of light energy with a small area of materials in an extremely much more effective method than just reflecting light onto something like a water boiler and then having the light either absorbed or reflected and dispersed. The idea is to have it so the light reflects continuously and stays in the trap for a long period of time instead of just doing work on only one hit. I understand that things that reflect light dont absorb heat so to speak. Such as black material getting hotter in the sun that white material. However, I have also had things like a chrome item sitting in the sun that was unbearable to touch because of how hot it got.

 

Kind of like so.

 

 

 

In the middle of the mirrors could be a plate that holds some medium to heat, but is also a mirror to reflect light back into the concave mirror so that it does not leave the trap. But the main question here is, can you trap an endless supply of light? Of course it will dissapate and warm up the mirrors but, really how much light can you get happening in the trap?

[Tormod]

My initial thought is, what sort of material would let photons in but not out?

 

And what sort of mirrors would give you 100% reflection?

 

Just wondering.

[arkain101]

My initial thought is, what sort of material would let photons in but not out?

 

And what sort of mirrors would give you 100% reflection?

 

Just wondering.

 

I assume you think I mean a light trap that traps light for good. This is not what I mean. I am refering to just boosting up the effect of light as a massive heat source.

 

It is not a matter of materials to let light in but not out. It is mainly just using a combination of mirrors so that a beam gets reflected into a somewhat closed system where the light has a greater tendency to stay than it does to leave. Relatively speaking a photon would bounce into the system and out in a matter of nanoseconds, however, the idea is just to get a few more bounces happening before it leaves.

 

You also dont need 100% reflection. In this idea that I am refering to. Any smooth mirror would probably do.

 

My main questioning is I guess, would this ( that is, trying to trap the light into a zone to do work) produce any greater heating effect than just using the mirror to simply aim the focus point at a boiler.

[freeztar]

My main questioning is I guess, would this ( that is, trying to trap the light into a zone to do work) produce any greater heating effect than just using the mirror to simply aim the focus point at a boiler.

 

Reflecting the light will not produce any noticeable heating effect. Heat is produced from light when a material absorbs it and the light changes to IR.

[modest]

I think I see what Arkain is saying. Focusing a diffuse light source at a small target doesn’t mean the target will absorb all of the available energy, especially if the target has a high albedo. Encasing it in something reflective would allow some of the reflected and emitted photons that have already interacted with the target a chance to interact with it again.

 

By my thinking, if a person had a one meter lens with some 300 watts of radiant energy focused at a small target then the target would successfully absorb some fraction of that energy. Of the fraction absorbed, some is radiated from the target in infrared. Encasing the target in a spherical polished metal mirror that reflects well through IR (leaving open an aperture for the focused beam from the lens) would certainly increase the percentage of 300 watts that gets absorbed.

 

 

I think this would efficiently use the 300 watts, but would not be efficient in an overall sense because it does not effectively use either the materials given or the energy available. The light source being diffuse means that more than 300 watts is available. The idea then is not to effectively use some given quantity, but to get the greatest quantity possible. Rather than using the polished metal as a spherical shell catching scattered and emitted photons, it could be used as a parabolic reflector catching new photons from the sun and focusing them on the target. This is a better use of the material because the photon flux from the sun is necessarily greater than the scattered and reemitted flux from the target.

 

As long as a person isn’t limited by the area where sunshine falls (such as being limited to a single window in a room), I believe the most efficient method would involve setting up as many focused lenses and mirrors on the target as possible.

 

Are we thinking along the same lines, Arkain?

 

~modest

[arkain101]

 

Are we thinking along the same lines, Arkain?

 

~modest

 

I would say yes. We are.

 

Only, I am thinking of scale and magnitude of this.

 

 

Instead of using an entire field of mirrors, I wondered if one could -by the methods we describe- increase the efficiency of a solar radiation energy system.

 

For example if we had two of these dishes pointed at each other and used a method to beam in a large amount of light, say from a lense or another parabolic mirror so that the energy is captured and the "heat" -infrared energy- does not escape from the system as easily. Many of the solar heat systems have the heating element and/or medium (such as boilers, pipes, etc) open to the elements, such as wind, rain, and air temperature. What I am suggesting is using mirrors to create a kind of partially closed system that acts like an oven increases the energy efficiency to "red hot" standards.

 

 

Here is a recent article about something similar to what I am talking about.

 

http://news.cnet.com/8301-11128_3-9868931-54.html

[Janus]

Here's the problem. The reflector you see takes light that comes in as parallel rays and directs it to the focus. If you place another reflector opposite it, the second reflector will block the light that the first reflector focuses. I don't see that there is any arrangement that could take light that enters from the side and cause it to bounce back and forth enough times before leaving, or efficiently be focused enough to be better than the one single parabolic reflector shown.

[Turtle]

This is something that I have wondered about quite often. What are ways you can trap light and if you can, can you have it doing work while it is trapped?

 

If you take a concave mirror: ...

 

I seem to recall reading something on using light traps to delay signals, but I can't find a reference right now. I did find a short treatise on light trapping that is similar to your descriptions however. >> http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TM-560.pdf

 

One thing that comes to mind is the cavity magnetron for generating microwaves, but I have no idea if light frequency behaves in an analogous manner. :) :)

[modest]

Instead of using an entire field of mirrors, I wondered if one could -by the methods we describe- increase the efficiency of a solar radiation energy system.

 

After thinking about it some more, I really think the field of mirrors idea such as Heliostat power plants and SEGS really is the most efficient way to go.

 

For example if we had two of these dishes pointed at each other and used a method to beam in a large amount of light, say from a lense or another parabolic mirror so that the energy is captured and the "heat" -infrared energy- does not escape from the system as easily. Many of the solar heat systems have the heating element and/or medium (such as boilers, pipes, etc) open to the elements, such as wind, rain, and air temperature. What I am suggesting is using mirrors to create a kind of partially closed system that acts like an oven increases the energy efficiency to "red hot" standards.

 

I think it's always more efficient to use any given mirror in a way that reflects new solar photons from the sun to the target rather than trying to catch scattered photons from the target. The only possible exception I can think of would be using something like a dichroic filter to encase the target which could be used to hold in infrared while allowing shorter wavelengths to pass. This would be like a greenhouse.

 

For all I know, solar power towers may already do something like that. I don't know much about solar power. But, as far as arranging two parabolics facing each other, I don't see how that would work.

 

~modest

[Zylatis]

thats pretty much a fabry perot cavity isnt it?