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Solar-powered laser (supposedly) Answered

 I was in this other forum about the Mythbusters' "Archimedes' Death Ray" thing. Our discussion went off topic, so I made another topic! According to Google, a laser is a device that produces monochromatic, coherent beam of light. We have established the coherent part of it by focusing the Sun's energy on point which has a mirror so theoretically, that focused part of the beam should reflect off the mirror. Our design(s) is/are based on multiple parabolas (or Fresnel lenses) to collect and focus light. The light is in turn reflected off mirrors to be combined on a mirror (or lens) which will be used to aim the light to the target. Unfortunately, I forgot the "monochromatic" part of the laser, but that's not a problem. All we have to do is put filters on our parabolas. That should be a cool enough part to filter the light without melting the filter(s) itself / themselves. What would be an idiotic thing to do is put the filter right in front of the last mirror, because it would melt it (unless off course, that filter was a pane of glass). 

 Any suggestions/comments/design ideas please put them up here. If your idea is just downright stupid (sorry, I don't know what else to use (other than idiotic, or crazy, actually crazy's better than stupid (back to topic))). If it is stupid, I will not use offensive words against you (unless you were swearing on my face); you will, instead, be facing the following words: "Sorry, your (insert suggestion/comment/idea) is not feasible. Please try again". I know it's a bit funny; part of it is for your entertainment, part of it is for your knowing. Again, please post any suggestion, comment, or ideas. By the way, if it's only a bit stupid, you won't be needing to face the words...

Have a nice day!



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nutsandbolts_64 (author)2010-09-11

Update: construction stalled. Must wait a few more months.

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nutsandbolts_64 (author)2010-06-01

Update: Construction of the small-scale prototype will begin on June 15.

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critterfluffy (author)2010-05-27

Here is a really good tool to play with basic optics principles:
http://dev.physicslab.org/asp/applets/opticsbench/default.asp

It seems you are having some trouble with it which is understandable.  The only reason I know anything is because I spent semester learing it with a teacher.  If you have any questions feel free to ask.

PS: The dots on the lenses are the focal points.  See what happens when you a lens with a long focal length and one with a short focal length and overlap them together.  What you see is the principle we are trying to exploit.

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user

Also notice that the smaller the ratio between the focal length of the two the tighter the beam gets.  It doesn't matter how big the lenses are, all that matters is the ratio of the two foci.

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 I noticed that. Now, all I need to do is persuade beehard44 to collaborate on the construction of a prototype solar laser (if he believes that it's gonna work at all). I'll design the parabolic collectors. The other half of the setup would be designed at a later date. 

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critterfluffy (author)2010-05-25

So how are things going?  Just thought I would check up since we haven't talked in a while.

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 My friend here (beehard44) is diverting me away from getting my parabolas. My sister used up all the ink last night so I guess I'm getting another ink cartridge (to print out the parabolas of course). I just discovered my current coil of galvanized wire won't stand up to the weight of the parabola support structure, and it was the last coil in that hardware store... Other than that, I'm about to begin construction of the small scale version (after my Aikido session today at 2:30 pm GMT+8)

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Sounds like you have been busy.  For the small scale are you going to go with parabolos for the collectors or fresnel lenses?  Fresnels would likely be cheaper but I am not sure.

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 During the proof of concept test, I have had mixed results. 

Result 1: I accidentally turned it into a projector.
Result 2: I accidentally turned it into a microscope
Result 3: Got it finally focused, but I didn't expect this to happen! (queue image)

Position 1: Shone the light at the magnifying glass. Focused perfectly!
Position 2: Hit the mirror at that point
Position 3: it just got dispersed! 

I believe we can solve the dispersal problem with another lens at position 3. At that point we're back to square 1! If that's the problem then that means that your design would look like image 2. What I don't get about your design is the final lens. My other test suggests that if a(n) (ordinary) lens has a light source coming in at an angle, that focused light would be on an angle. I'll test again. Confirmed... We need an unusually shaped lens to counteract what we see here. I'll come up with something sooner or later.

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user

Your picture shows the reason for the dispersion.  If the light is slanted inward it will reach its Focal point and then begin to disperse.  The flat mirror doesn't affect this at all.  It does need another lens to prevent this.  What you do is place the two lenses so their Focal points are in the same place.  This causes a beam to form.  That is why in my design there is a lens in the parabola.  The parabola collects all light to a focus.  The lens takes this light and focuses back to infinity with a smaller cross-section.  That is all there is to it.  The key is crossing foci.   
Simple image(no time to make a proper one)
===()><()-------

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 I'm not an optical physicist, but that's understandable. That reminded me when I wanted to see magnification with lenses. Is magnification an example of what you're talking about?

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Its the same principle.  The idea behind it is you get two lenses.  One has a focal length of 2 inches and the other has a focal length of 1 inch.  This causes two times magnification.  If you run this in reverse the image gets smaller. 

If you set this up to create a beam, the affect is the light entering is 3 inches acrossed(assuming the lenses are 3 in diameter) and comes out 1.5 inches acrossed. What we are doing is using a dish that has like a 12 inch focal point and a lens with a half inch focal point.  When positioned correctly this causes the beam to be 24 times smaller or 24^2(576) times more intense.  There will be some abberation but at short ranges this is negligible.

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 Unfortunately, I only have a 1 inch diameter lens for that. According to my calculations, the light would only be 144 times more intense. If I multiply that to the temperature on my part of the world, I would get 5184! If I run it through 576 then I'll get... It would be 20000+! But we don't need something that'll vaporize aluminum. All we need is something that'll burn wood. A 1 inch lens should do. Also consider it a fire hazard, so I'm using a flashlight just to be safe. 

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***This post is in regards to my other post(probably below).  I cannot reply to my own post and I realized I left this information out.***

Basically, what Watts/m^2 means is the ability to do Work(in this case temperature change) to a given mass over a period of time.  When you multiply this you are increasing the speed in which you can heat something up.  In the case of our deathray we are multiplying it by sacrificing surface area to get a more intense light.

PS: The only reason something will stop getting warmer is heat is constantly lost to the environment.  Air will be robbing your target of heat.  Since, as things get hotter they lose heat faster to its environment there will always be a point where energy in equals energy out.  This is what determines the hottest you can get an object.  Also, this means that as you approach the equalibrium point you will be heating the target up more slowly.  There is an equation to calculate this energy loss to the environment base on material but I do not know where to find it, I just remember learning it in my thermodynamics class in college.

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For lenses, all that matters is the ratio of focal length between the two lenses used.  This determines the level of increase in intensity you will receive.  A flashlight will work, sort of, for a small scale.  The only problem I forsee is light coming off of a flashlight is not perfectly parallel.  This will cause a lot of abberation.  This is fine for a small scale test but when you see abberation in your tests be aware that it is likely from your light source not the device. 

As for you calculation, I am assuming your temps are in Celsius since you hail from a country that is smarter than the USA when it comes to units of measurements.  (I seriously hate that we don't use metric here)  It doesn't step-up ambient temperature since it seems that is where you numbers are coming from.  What it is about is power in Watts/m^2.  Sunlight, unmodified, averages about 1400 Watts/m^2.  This is what you will be magnifying. 

Here is a simple example of how it works(numbers made up). 
Put 1 kilo of ice out in the sun.  It is about -10 celsius.  Lets assume It takes 30 minutes to fully liquify.  This means 1400 Watts/m^2 will raise water 10 degrees in 30 minutes.  With 144 times intensity, it will take 144 times less time to do the same work.  Roughly 12.5 seconds to melt 1 kilo of ice.

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 Likely. I have no single idea where to get small Fresnel lenses in a 5000 mile radius around my current position. I'm gonna substitute the Fresnel lenses with ordinary ones. All I need are some magnifying glasses... In the other room... Gonna get my keys... 

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critterfluffy (author)2010-04-17

So we were discussing the solar death ray in the previous thread.  I have been thinking about the mirror setup and I think I have a workable idea.  So the problem that is very common with this type of setup is how to you aim the light collected from the sun effectively throughout the day even though it is moving.  This is easy to do if your target is standing still but doing this while the target is moving is nearly impossible.  The answer is a stable collection system that focuses everything to a single point and at that point is a final mirror/lens used for targeting.  I am working on a diagram for this and I will post when I have it drawn up.  It wont be cheap for the full scale product but that will probably never get built.  The small scale would be 2 collectors and a focuser.

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 I don't understand the "focuser" part because the collectors focus the light, or are you talking about the final mirror/lens? Either way, the small scale prototype should be done with a constant, artificial, heat source. Incandescent light bulbs should work, or just a fire suspended in mid air. This is due to unpredictable weather, but if you got a nice sunny day you could set fire to a sheet of paper out in the open for realism. If the paper catches on fire then you could say that the heat being generated is above 200 degrees Celsius. If that's the result on the small scale then there should be no problem with the large scale where you have greater surface area. And the simplicity would make it confirmed, if not plausible, to the Mythbusters. 

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Sorry it is taking a while to get back to you.  I have been looking up some of the equations and physics of optics to write up something that should work.  I am trying to make it easy for people to concentrate light using multiple mirrors and then allow for easy, one step targetting/focusing.  It is taking me a while since it has been about 5 years since I last studied optics.  Having trouble finding good reference materials(especially for a parabolic mirror).  Though, from looking around a hyperbolic mirror would be the best and most expensive solution.

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 I, this time, am sorry. Sporadic schedules and the like. Anyway, that means we're going with the original design, only slightly modified. I don't think it would be so expensive to get a hyperbolic mirror, if we were using rudimentary materials. Otherwise, we'll just get a giant Fresnel lens from those projector TV's, and use that. 

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I still think the Fresnel lens is definitely the easiest and cheapest but the other idea I am working on is more in line with Archimedes.  Basically there a lots of smaller mirrors collecting light and sending it to a single point.  At that single point is a system that allows the light to be redirected and focused within a range or angles.  This way the small mirrors just have to redirect light to the collection point and then everything goes from there.  I don't know if this is possible without a computer controlling minute changes but that is what I am trying to find out.

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 Anyway, I got an animation of the solar laser on the parabola version.

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the problem with that image is with the focus of the beam.  After it reflects off of the parabolic mirror it hits a flat mirror.  This would not prevent the light from pulling away from being a beam.  I have been trying to find a way to remedy that with either a lens or a spherical mirror.  I do like the simple flat mirror at the end but that would create one heck of a hot spot.  you might be able to bring the beams in at an angle on the flat mirror to have them meet at the target.

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One heck of a hot spot on what, the mirror or the target? 

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Technically both.  The flat mirror used to direct the beam at the target is taking all of the light in one spot.  This would heat up the mirror quickly in one spot.  Like I said, you could send the light in at different angles spreading the light out and then focusing it on the target using those angles but that means to focus you have to move all of the collectors.  Check out the picture I linked, it solves both of these problems.  I couldn't upload it unfortunately.  Also, sorry about being a little confusing sometimes.  I tend to have a problem with that.

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 What doesn't make sense to me is the parabolic targeting mirror. That would limit the range of the whole system which what the original system is supposed to solve which means we go back to square one. The only two solutions I see is either we use an extremely reflective mirror which means most of the heat will also get reflected off thus increasing efficiency, or just plainly take the heat. So it's either cost or quality. Otherwise, make an animation that shows what you're talking about.

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I finished an animation of how the assembly would work.  It doesn't show it, as I cannot think of how to animate it, but the top assembly can be rotated horizontally around the focus to allow for full range targeting.  Since the light coming from the lower half is always coming in vertically the top flat mirror will always send the light into the targeting parabola at the correct angle allowing it to be focused.  This could easily be computer controlled for accurate targeting.  This is about as simple as I can make the whole device.  The advantage of this system is it allows for as many collectors as you have room.  Hope this helps.

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 Haha!!! Just on queue! I found an instructable that shows me a site that plots parabolas for me. 

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"have" in my post should be read "half".

I need to proof read more.

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user

If you wanted to, you could also replace the collectors with a Fresnel lens that focuses light initially into a second lens to create the beam.  This would replace the parabolic mirrors used for collection.  You can get large Fresnel lenses from big rear projection TV's.  These are not that hard to find depending on your area.  Also, be aware that the focal point on the targeting parabola should be long and the flat targeting mirror needs to be bigger than the lower flat mirror.  This will prevent two things:
1.  As the top two mirrors rotate, the flat mirror might come in contact with the parabolic mirror.  This can be seen on the animation.  This is cause because the flat mirror always rotates have the angle of the parabolic one.
2.  As you aim the final beam down, the rays may begin to miss the flat mirror and either shoot up into the air or hit the parabolic mirror.  If the parabolic mirror is hit, the path would be unpredictable(sort of) and anything might happen(most likely bad).
Also, as a safety you can add a flat mirror that can slide in and out from between the bottom and top assembly.  If perfectly flat, this would cause the beams to reverse their path and be shot back into space.  This could work sort of like a safety so the beam isn't accidentally shot.  Neighbors tend to frown on burning down their houses.

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 The animation works without a hitch at all. Now I understand. It's getting more and more complicated week after week of this discussion. I wonder if the mythbusters will accidentally stumble on this forum and make another revisit episode. All I need is a parabola and more wire and I can get on with constructing it.
_______________________________________________________
The following is an off-topic topic:
This proves that people can understand complicated things better with animations and/or videos.

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I don't know how to make an animation.  What did you use to make yours?  I will see what I can do though.  Also, the system I have would allow 360 degrees of targeting and up and down panning for targeting different altitudes.

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 I just used MS Paint and Gifted Motion. Click here for the download. It's located on the bottom most part; it's labeled gifted motion.jar. It's size is 67KB since it runs off java. Just google it. 

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 I just used MS Paint and Gifted Motion. Click here for the download. It's located on the bottom most part; it's labeled gifted motion.jar. It's size is 67KB since it runs off java. Just google it. 

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Had an idea after looking at your design.  It takes advantage of a property of a parabolic mirror.  Anything that passes through the focal point will be reflected out to infinity, essecially reversing the path that makes them useful in telescopes.  By using this all you have to do is use your collectors to send their beams through a hole punched through the center of a mirror positioned at the focal point.  This will allow said mirror to then redirect the light in parallel beams to a targetting system which is nearly identical to the collecting system.  The only difference is the targetting parabola and mirror are movable and the focal point has a lens.   This, when the system is worked out, will allow any number of mirrors to collect light and accurately target a ship on the sea(even a moving one).  This also removes many of the super hotspots in the system.  The only part that has to be really precision is the final lens and lenses loose less energy to heat due to light so it should be fine.  I don't think the picture is going to add so I am going to link it to be sure.  Work uses IE6 still so it doesn't like to add pics to comments.  HERE is the picture.

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 It is possible. If you're talking about rotating the whole rig that is. Just put some gears here and there. Get some gear reduction going. The focal mirror will have some little hydraulics on it to enable aiming of the focal mirror to the combining mirror. 

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Kiteman (author)2010-04-26

Launch a satellite.

The satellite charges capacitor banks from solar cells, then (eventually) dumps the energy through a very large laser.

Drill a hole through the ship; sink the ship.


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nutsandbolts_64 (author)Kiteman2010-04-26

 Now where am I gonna get a MW laser? Maybe I should get some from the Russian Mob! Seriously  though, they also have access to Cold War era subs, and they include missiles. 

Note: There is a documentary film about the Russian Mob, so the information above was already released via the said film.

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