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Solar laser? Answered

So recently I've collected a couple 32" fresnel lenses from rear projection tv's and am curious how one( if possible) would collimate the light into a laser beam to cut materials. I've spent a few hours searching the web trying to find the information I am seeking. Even help with searching terms would be appreciated.


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1 year ago

Laser = coherent light. Means: All photons are in synch in their wavefunction. All "Dance in unison". Same speed (EXACTLY and only ONE frequency of light!) and same phase.
Sunlight = Non coherent light. The phase of all photons are pure random as well as all the frequences are present. It is hard to go further away from a laser than the sun...
Laser = Abbreviation for "Light Amplification by Stimulated Emission of Radiation". Wich imeans YOU have to amplify light somehow.
Sunlight, colminated = All photons are already there. From the sun. No need to amplify.

Long story short: You cannot create a laser from sunlight with reasonable means... Or you invest in some VERY fancy phase-correction/filtering of photons.

However, what you propably wanted to ask:
"Is there some way of culminating sunlight into a almost 0° spread?"
Sure there is: Fancy and expensive optics. Be sure they are super-efficient as with the many 100W to 1kW you are dealing, even 10% loss due to optics will have quite bad consequences for the optics involved.

As a startingpoint, you may check a few of the threads over at https://www.physicsforums.com/threads/collimating-sunlight.729272/ and the suggested other threads at the bottom.

Edit: A good point is also astrophysics:
Especially https://www.handprint.com/ASTRO/IMG/geolens3a.gif
See, for your needs, you can assume the rays from the sun are parallel. They get focussed by your fresnels at the entrance pupil. Now you need to build the optics in the exit window as shown. Better you read up on optics and optical simulation. Its a topic i avoided as engineer.

Edit2: As a good starting point, read up on this paper: https://www.osapublishing.org/DirectPDFAccess/415C...
It may give you a first insight of what you are diving into.

Check the comments and links at https://www.instructables.com/community/solar-ligh...

Jack A Lopez
Jack A Lopez

1 year ago

Well, I think what you want is a diverging lens (also called concave lens) placed near the point where the rays of light from your big Fresnel lens converge, and that diverging lens will serve to bend the rays back towards parallel, but in a smaller beam than the diffuse beam of natural sunlight; i.e. the beam having area of the same size as the giant lens.

Note this is essentially the same arrangement as a Galilean telescope,


which consists of two lenses: a converging (aka convex) lens followed by a diverging (aka concave) lens.

By the way, the telescope design made from two converging lenses, is called Keplerian. This design has certain advantages, as a telescope, compared to the Galilean design, and for this reason it is a design you can find still sold today, if you go shopping for a cheap refracting telescope. One notable disadvantage of the Keplerian design, is that it turns the image upside down.

I am not sure what arrangement is used in a typical pair of binoculars, but at least those leave the image right side up.

Sorry for the diversion into telescopes and binoculars. Getting back to your problem of straightening out converging rays of light, I think the Wikipedia article for "Lens"


is worth looking at, because it explains converging and diverging lenses, and some of the formulas for working with these.

Also I wanted to warn you about calling the resulting small, collimated,


beam a, "laser beam."

The reason why is because it will very temping, to those people who know all about lasers (i.e. coherent light produced by stimulated emission) to tell you all the reasons why what you are contemplating is emphatically NOT a laser beam, and why it never ever could be, etc..

Call it, "laser-like, " or "like a laser beam," if you absolutely have to include the word "laser." I think you might possibly avoid getting into pointless arguments that way.

In truth, what you want is a collimated beam (i.e. beam with parallel rays) of sunlight, but just one that is much more intense.


1 year ago

What materials? Steel? It would be very hard to cut accurately, and would create a ton of smoke.


1 year ago

You can't.
What you can is use a lens to vreate an intensly hot and bright spot though.
But it requires tracking of the sun because the damn thing won't stop moving around ;)

If you want to try cutting stuff like cardboard or thin sheets of wood you need to work in reverse.
Means you are not moving the light source but only the object you need to cut.
A major downside of fresnel lenses is that you need a sturdy frame to keep them flat.