Basically I have wondered this for a while... The sunlight can be concentrated to the point it is incredibly powerful, but traditionally this is only at a focal point after which the light rays "fan out" again and there is no intense heat. What if I want the light to stay concentrated over a distance? Technically a fiber-optic like setup (B) should work to keep the light concentrated in the cylinder as long as it is sufficiently small in diameter, but as soon as the light exits the other end it would disperse again as the angles of the light rays stay the same and just reflect off of the cylinder walls. Is there some kind of prism, polarizer, or other component I could use to straighten out the light rays once they are concentrated by the lens?
How could I get the light to stay concentrated
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Sunlight has multiple wavelengths, phases, and polarization angles that interfere with each other. That's why we invented lasers.
Power a lazer using a solar panel.
Lol, that's the literal answer... but what if I can tolerate a little bit of light lost - is there a way to form a *relatively* tight beam that would stay a beam for say, a few meters? One meter? There are some big lenses like those made of TV components that produce so much concentrated light that even a 80-90% energy loss in a somewhat tight beam a few meters out would still leave a seriously hot beam.
The reason laser beams can stay concentrated is because the light is monochromatic, and in phase. Light from the sun would slowly diffuse because the different wavelengths interfere with each other.
Read this.
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I'm not trying to make a laser though... just to keep the sun beams together for a short distance - just further away than right at the focal point.
A collimator would basically defeat the purpose of concentrating the rays down to a small point, unless they could be somehow otherwise set in generally the proper trajectory before hitting it, which is what I'm trying to do - to straighten out the beams on the other side of the lens, even if for just a short distance, at a higher concentration than when they go in.
go learn some EE senpai incident light from our god the Sun has many frequencies which means youd need to use a prism that somehow dynamically converts random incoming light to the correct vector which with nanoscale materials in a mobile solution might be able to do (quantum dots?) shits hard senpai and aka EXPENSIVE
Laser beams spread out over distance just like any other light source.
You can't do that with passive optics because you need somewhere for the entropy to go. You can power a laser with sunlight, though. No need to convert it to electricity first.
> because you need somewhere for the entropy to go
It had been my understanding that wherever the photons ended up hitting would be where the entropy went. They would still be converted to heat...
If you've converted them into that narrow beam in OP's pic, you've already removed the entropy in question.
Concave lens, obviously.
yes OP, it is possible in theory, however in real world you will lose 80% of the energy by heating up the cable, therefore changing its refractive index, therefore probably breaking it
also keep in mind the rays will spread out randomly once they leave the optical fiber
You didn't even understand his question, dumbarse.
If you want a coherent white light lazer it needs to be created by multiple colors lazers r,g,b and combined through a prism. Unfortunately it's not a true full spectrum light.
This is obviously the correct answer and everyone in this thread telling OP he can't do it is a fucking moron.
You could invent new laws of physics for an alternative universe, or you could listen to what's already been explained to you multiple times. Your choice,
Gosh, how could I not think of this... if I mounted it a set distance from the convex lens, preferably right before or after the focal point, it may just produce a beam of the kind of intensity I would like... Now I am itching to get my hands on one and do an experiment...
I'm assuming you're talking about plan (B), in which I would intend to use very clear glass that the great majority of light would pass through... maybe closer to 20% lost in heat, and it wouldn't all be at one point so it probably wouldn't change the refractive index to the point of messing up the experiment.
I don't want a lazer and I've pointed that out a couple of times lol... if I can get it to work properly, pretty much answers my questions. It bends the cone of light from the convex lens into a straight line, which is what I've been trying to figure out how to do this whole time.
>I don't want a lazer and I've pointed that out a couple of times lol.
You could though, look up white-light Generation.
You need an ultrafast laser though, so thats probably harder to get than sunlight.
pls post result if you do
What are you going to burn? Wouldn't the practicality of a long-range solar burning setup be limited by your ability to place your lens arrangement between the target and the sun?
First of all it's not long range as in the distances a gun would shoot, just maybe a few meters if I'm lucky. Also, if the beam held together well enough I could place the focuser setup in optimal alignment to the sun and then use mirrors to redirect it. As far as what I want to burn... I have a couple ideas but don't want to spoil something patent worthy if it ends up working lol, nothing nefarious like pic related - though certainly even if it's just a glorified ant toaster it would still be fun.
I'm looking at lenses on Amazon but may not order one until I find what focal lengths I need... anyone have a better understanding of this? Could I get any pair of convex and concave lenses and adjust the distances between them until I get the "beam"? Certainly I think I would need glass and maybe higher quality product for the concave lens at least due to the heat involved. Then I would need a frame...
Hey it looks like I don't even need a concave lens if I put it AFTER the focal point...
Yep. Hey, OP, are you going to post results?
If I actually get the parts and build it... I'm just sitting on my computer right now and was trying to solve this problem... now that I have, I have to get up off of my butt and shell out some cash for the components. How long do threads stay up on this board?
Just use a laser you dumbass.
>yet another brainlet trying to tell OP to use an expensive laser to do what two cheap lenses can accomplish
Holy fuck Veeky Forums sucks at science.
Uh, I think it's impossible due to the laws of thermodynamics, actually
One principle is you can't get things hotter than the surface of the Sun. Otherwise an optical system would move heat from a colder region to a hotter region without adding any energy, effectively breaking the second law of thermodynamics and enabling infinite energy.
Meme or not, Randall Munroe discusses the matter pretty well: what-if.xkcd.com
>this is literally a regular occurrence in microscopy and it took us this long to reach here
We're idiots, Veeky Forums.
I was gonna say use a regular lens over the Fresnel because muh chromatic aberration but you know what, on your scales the Fresnel is probably a better choice.
Also beam spot size is then limited by second (condenser) lens focal length I suppose? You could then set up an array of condenser lenses to control beam spot size.
He's not violating anything, what OP is doing is increasing power per unit area by decreasing area, not magically adding photons to our system.
The law you're trying to cite works on a scale far larger than "compressing the photons to increase power density".
Pretty slow board. Maybe a combination of photographic lenses would suit your purposes? The Filmmaker IQ YouTube channel had some interesting videos about how lenses work.
this won't work OP, can't you really see it?
Wait, isn't that basically how a fucking telescope works? Just adjust the focal length ratio and you're good to go
Lol this - as if I will shell out $100,000 for a laser actually hot enough to burn anything beyond styrofoam cups when I could make something more powerful at closeish range with $50 on Amazon. Also maybe I am interested in concentrating and collecting energy rather than blasting it out by the megawatt and getting a whopper electric bill.
It looks like the physics add up so far, still waiting for a sunny day and the parts to test it. I don't expect to make something that melts stuff half a km away, just a beam that I can sweep around or focus on something a meter or two out.
I am starting to wonder now if a device could be put together that tracks the sun with the concentrator lenses automatically (computerized with Raspberry pi maybe) using well established sun tables and geographic coordinates, or otherwise a sun polarity sensor of some sort, and then has an adjustable array of mirrors that allow the beam to be pointed in the desired direction irregardless of the sun's position... that would take this from being a neat science project to being pure awesomeness.
>I am starting to wonder now if a device could be put together that tracks the sun with the concentrator lenses automatically
Absolutely. Astronomers build this kind of thing for their telescopes all the time. Look up what sort of solutions they devise. I'm sure many of them hack together something with raspis, but there are also commercial solutions.
Collimate the light. It's different from focusing. Requires two lenses.
What you are trying to do is probably impossible(barring making a solar pumped). Before you do anything else look up conservation of etendue
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Different wavelengths refract at different amounts in the same medium. Its why rainbows are a thing. Using a prisim you will never straighten out all the colors of light, because causing one wavelength to straighten would cause ALL of the other ones to bend at different angles.
That's what I was thinking at first, but all that means is that the new beam has to have a larger angular spread than the original sunlight.
Which just places a limit on the range of the thing.