# Sunlight collecting lens coupled to fiber optic cable (laser)



## marshall (Oct 13, 2005)

I've been thinking about building a tripod setup which collimates sunlight from a 7" magnifying lens into a very small diamter output, which would be coupled to a 6 ft. fiber optic cable. I'd then like to have a re-collimating lens on the end of the fiber optic cable, so that it would not just scatter upon emission.

Does anyone have ideas of what parts will mate easily (such as correct fiber optic cable I should look for, collimating lens's, and possible lens holders etc.)?

I'd appreciate any help on this project.

Thanks.


----------



## HarryN (Oct 13, 2005)

For a collection lens that large, I would start with a platic Fresnel type. They are a lot lighter, fairly efficient, and reasonably priced, especially in molded acrylic. They are often sold as solar panel concentrators.


----------



## bootleg2go (Oct 13, 2005)

It would be a fun project to build, but will not result in a laser. What you will have is a bright flexable solar powered flashlight. Unless the light is "coherent" ie the wavelength/s are in phase, the light will quickly scatter just like a normal flashlight's beam does.

Jack


----------



## marshall (Oct 13, 2005)

bootleg2go said:


> It would be a fun project to build, but will not result in a laser. What you will have is a bright flexable solar powered flashlight. Unless the light is "coherent" ie the wavelength/s are in phase, the light will quickly scatter just like a normal flashlight's beam does.
> 
> Jack



Ahh, I expected barriers in this idea (didn't even stop to think about coherance), this might be the main project stopper. Shows my lack of photonic knowledge in this concept. The main use for this was going to be practice with laser wood etching/engraving. Is there anyway a coherant wavelength could be filtered from the multi-wavelength sunlight? Would it be useful for etching purposes at close distances (0.5-6")?

Edit: Also, could the light be focused to an extremely small beam diameter upon exiting the fiber optic cable (say 1.5-2.5mm)?


----------



## PhotonWrangler (Oct 13, 2005)

It's not a matter of filtering; the sun's rays don't include any coherence at all, at any wavelength. To get coherence you have to make it from scratch from a resonant cavity with optical gain and mirrors on the ends. The LA in laser stands for Light Amplification, and unfortunately you can't get that from a set of passive filters.


----------



## Athoul (Oct 13, 2005)

However you might be able to use your idea and get the sun to act as a pump for a lasing material.


----------



## fstower (Oct 13, 2005)

Odd, I always thought sunlight was at least very collimated...
It's multifrequency but insanely collimated!
You should be able to at least do some very interesting things with it.

It's far better than a 'flashlight'

Take a small mirror and reflect the light to a place 100's of feet away....


Hmmm.... how much does the light beam spread out?

Hardly at all!!!!

Steve


----------



## Athoul (Oct 14, 2005)

All light will eventually become more coherent (I believe) over a long distance. Light that travels from a star over a long distance is more coherent then when it first leaves the star. Laser light travels over a very far distance (back and forth in the laser cavity) and when it exits the lasing medium it is coherent. However I don't think light from the sun is collimated..I could be wrong.


----------



## badhorsey (Oct 14, 2005)

Now I'm thinking in terms of the Pak Protectors' laser defence in Larry Niven's Ringworld Engineers (in fact, reading Ringworld at the age of 12 was the thing that started me wanting to have a "flashlight laser"... and now, with my 55mw greenie, I have one! But I digress.)

The thing I'd like to know was why did it lase in violet?


----------



## HD58PHD (Oct 14, 2005)

I think maybe you should consider the fact that collecting enough solar power to burn might also melt any fibre link and optics used.
Maybe a better and easier approach would be an x-y marking system using a large magnifying glass and collimating optics to focus onto the scanning assy?
We know the potential is readily available,a few mirrors,reflectors(parabolic)and a couple galvo's from e-bay and were off!


----------



## bootleg2go (Oct 14, 2005)

Athoul said:


> All light will eventually become more coherent (I believe) over a long distance. Light that travels from a star over a long distance is more coherent then when it first leaves the star. Laser light travels over a very far distance (back and forth in the laser cavity) and when it exits the lasing medium it is coherent. However I don't think light from the sun is collimated..I could be wrong.



The distance light travels does not make it more or less coherent. Coherent means that they are in phase (all the peaks and valleys of the waves line in perfectly). If takes a laser to make coherent light. Even over light years of distance the individual particles of light will not speed up or slow down for them to line up in phase, the speed of light does not change going through space. In fact I don't thnk coherent occurs naturally at all, it has to be created.

Jack


----------



## James S (Oct 14, 2005)

While it wont be a laser, that doesn't mean that it might not work for the stated purpose of wood burning. I dont believe you could get something hot enough to actually cut the wood, but just to burn designs into it or whatever, like what you do with a soldering iron might work.

Or it might not  You might just end up melting the end of the fiber that you focus the beam on. I'd think that you might want to use glass fiber rather than plastic to avoid that.


----------



## bootleg2go (Oct 14, 2005)

For wood burning it could work.
You could use a large lens to concentrate the light from the sun down to the diameter of the fiber optic cable and then at the other end of the optic cable have another lens to fucus down to a fine point for burning.

Jack


----------



## HarryN (Oct 15, 2005)

With even a 2 inch magnifying lens, the spot intensity is sufficient to burn / engrave wood. In fact, the brightness is such that you really should consider welding goggles when doing this project.


----------



## marshall (Oct 16, 2005)

Jeez, no offense, but come on...you're all giving me obvious info on the most basic levels, and starting non-pertinent debates! 

I really appreciate the help guys, and I'm not trying to come off as a jack-*** (as I probably already am by speaking bluntly), but I think I should be able to take it from here on my own (this thing is simple to do, and you're telling me I can't cut wood with the sun...pshh!). 

I was mainly looking for manufacturers offering capatible parts, I'm schooling as an astronautical engineer, I know some "basic" photonics-direct related properties, but I was mainly looking for help in finding appropriate compatible parts as I know the thermodynamic properties/efficiencies of what I'm working with etc.

If compatibility options for this to work will cost me an arm and a leg, or master fab work and $ (which I doubt it will considering what's needed), then this "hobbiest" project will be ruled out and forgotten about. As I said, I'd just like to aquire wood etching/burning technique practice, and thought of a quick way to deliver light energy without actually "lasing" (I know I know, I forgot this is not a light amplification process, but I still feel this is probably the best forum area for the given topic).

Edit: As for the welding goggles in conjunction with this project...you got that one right!

Thanks a lot for any added info guys!


----------

