Is it possible to make a "laser" etcher using "piped" sunlight?

[some bloke]

Summary:

I say "laser" in inverted commas as my goal is not a true laser but an intense light which can burn the surface of wood, leather etc from focused sunlight. "piped" refers to reflecting the sunlight down a fiber-optic setup, of some sort.

Main Question or Discussion Point

This is an older idea of mine which I just remembered when reading the thread about using a light-bulb to make a laser.

The concept is this:

1: Focus light from the sun into a point using a magnifying glass, which we know can burn things.
2: at the point of focus, place another lens which will (roughly) re-focus the light to be mostly parallel (if necessary)
3: direct this much more intense light through a fiber-optic cable to the business end of the engraving tool
4: Said intense light comes out of the end of the cable, to be pressed against something to be engraved such as leather, wood etc).

My main query, I suppose, is whether it is possible to transfer the intensity of focused light from the sun through a fiber-optic cable. I'm assuming the end of the cable will heat up, which means that heat isn't transferred and that the other end, whilst bright, will not possess the burning quality of the point from a magnifying glass.

I haven't found anything like this online so I don't know if I'm just missing something obvious or onto something new! (I'm assuming the former...)

any assistance and guidance will be appreciated!

 

[sysprog]

No, that's not how lasers or 'light pipes' work -- nice idea, but, no.

 

[Baluncore]

any assistance and guidance will be appreciated!

The primary mirror would need to be large and accurate. The incident sunlight will have an 0.5° of divergence due to the apparent diameter of the sun. The problem then will be with the secondary optics that converts the convergent sunlight into a very fine parallel beam for insertion into the fibre or light pipe. The lens mounting at the point of focus will melt as dust and pollen from the air settles on the surface. You would need to use a secondary mirror rather than a wavelength sensitive lens. Maybe replace the primary focus optics with a logarithmic tapered horn, probably with an iridium plated and polished internal surface to funnel the light into the fibre. Designing that horn with a minimum number of internal reflections prior to light entering the parallel tube will be a real challenge.

You would do better with a real laser module powered by a PV panel. The PV is less direction dependent than an optical system, and can have a greater area than the precision primary mirror otherwise required. Another advantage is that it will work at night when you run the laser from an alternative power source.

 

[some bloke]

Thankyou for the replies!

This is more of a challenge than an effort to make the best engineered product I can - as said, an electrically powered laser module will serve the purpose best.

The lens could be stored in such a way that dust & pollen could not get to it - like the lens arrangement in a pair of binoculars or a telescope - would it still be prone to melting if it was within a sealed unit?

Cheers!

 

[Baluncore]

The lens could be stored in such a way that dust & pollen could not get to it - like the lens arrangement in a pair of binoculars or a telescope - would it still be prone to melting if it was within a sealed unit?

If the lens was in a sealed space it would not be cooled by convection, so it would probably get quite hot. You could arrange a forced air circulation sytem with filters. You have some significantly difficult problems to overcome.

 

[some bloke]

My main concern is the actual feasibility of the endeavor - I don't want to go through the nitty-gritty of solving issues like dust build up and cooling if the end result could only ever be a fairly bright but otherwise useless light!

 

[Baluncore]

I don't want to go through the nitty-gritty of solving issues like dust build up and cooling if the end result could only ever be a fairly bright but otherwise useless light!

Design 3 quite different ways to collimate the convergent light from the primary mirror and inject it into the light pipe.

Go through the energy accounting and see if the numbers are practical.
Here are the questions.
How much energy do you need to deliver?
What wavelength band can you use?
What % losses will occur in the light pipe at different wavelengths?
What area primary mirror will you need to gather sufficient energy?
Will you have a heliostat track the Sun, so the optical system can be fixed? https://en.wikipedia.org/wiki/Heliostat
How big will the heliostat mirror need to be?
Do you need to reject energy you cannot use, to avoid overheating?

 

[jamesson]

Useless googling pays off

https://www.febo.co/

 

[some bloke]

Useless googling pays off

https://www.febo.co/

That's only the first step of what I want to do - what you've found is a magnifying glass with a jig to hold it at the height of it's focus point from the paper.

I'm hoping for something I can set up in a window, and then transfer the energy via fiber-optics into the room, where I can sit at a desk and use it.

 

[trurle]

That's only the first step of what I want to do - what you've found is a magnifying glass with a jig to hold it at the height of it's focus point from the paper.

I'm hoping for something I can set up in a window, and then transfer the energy via fiber-optics into the room, where I can sit at a desk and use it.

Would i make such contraption, it would be built as follows:
1) Fixed Fresnel lens panel - cheap, easy to install and maintain
2) Automatically movable focal point with PD quadrant detector, microcontroller and two stepping motors.
3) Endoscope-grade fiber cable connecting movable focal point and workplace.

The performance would still be inferior to laser, especially in spatial resolution and energy output consistency. Not very useful for burning a precise patterns. But may be ok for tasks like irradiating UV-hardened coatings.

 

[bobbyburger]

This might be helpful.
https://www.sciencedirect.com/science/article/pii/S092702489800083X#bBIB1

 

[berkeman]

This might be helpful.
https://www.sciencedirect.com/science/article/pii/S092702489800083X#bBIB1

Welcome to the PF.

Interesting link, thanks. I wonder how long their fibers were when they got the 60% efficiency number...

We report on a flexible light guide which consists of 19 optical fibers and is capable of transmitting up to 60 W of optical power, with 60% efficiency.

 

[Baluncore]

This might be helpful.

Unfortunately that paper is behind a paywall and Elsevier want $40 for a copy.

The abstract should have identified how the light was converted from convergent to parallel prior to insertion into the fibre. What was the angle of convergence at entry? What is the fibre material? Does the fibre have a graded index?