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Focus a laser-like beam from LED(s)?

Is it possible to focus a beam from an LED so that it makes a laser-like beam? Could it be made to burn? I've heard of simulated lasers that sound like they use LEDs focussed into a beam.

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frollard6 years ago
I'd be curious to see what happens if you fired an led through some optics that concentrated the beam down to less than 1 degree. Theoretically possible, but the precision and cost would be WAY above the abilities of the average diy'er. Imagine then a bunch of those beams collimating in a giant laser assembly of doom.
ARJOON frollard6 years ago
yeah i've been trying it with a 1 watt led. passing it trough big oprical fibres. it stretched it so that it becomes small at the other end but no success. also tried with lens from a telescope but still no success. lack of accuracy
frollard ARJOON6 years ago
My though is led 180 degrees to a parabolic reflector to make parallel beam lines...

then take those parallels down with a fresnel (if thats possible) or a LARGE convex to bring it to a point...

then at that point have a concave to make them parallel. I think it can be done - but again needs ridiculously accurate optics.
ARJOON frollard6 years ago
yeah sure. but howerver it would cost cheaper than the 1watt laser cutters in big industries still accuracy is a problem. another way would be manufacturers who woulld make an led that just focus all the light in less than 1 degree. if they are able to make light dispersing in 60degrees or so they should have overcome a light dispersion within 1degree plus or minus 0.3

I would pay for the expenses if anyone wants to do this with me. I'm working on a project that requires an LED to act like a laser. The problem is collimating the light correctly. I live in New York if anyone is interested.

JCR

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NickL72 years ago

It depends on what you mean by "laser-like", and what you're willing to give up to get that result.

There's a conservation law in optics: the product of the solid angle and the area of a "beam" can only get smaller as you go through an optical system if you lose energy. (For the equation-minded: http://en.wikipedia.org/wiki/Etendue) To go from a 2mm^2 by 120-deg (half-power angle) LED to a 0.1-deg collimated "laser-like" beam without losing energy, the resulting beam would have a 0.8m diameter beam -- for example. Smaller beams with a tight angle are possible, but you necessarily have to lose light to achieve those beams.

Focusing an LED can also be challenging, since many LEDs start out with a large angular spread. My hint there is to use a large lens (to capture more light) with a short focal length (what optics calls the "numerical aperture"; the larger the NA, the smaller the possible spot size).

Burning is going to be challenging, in general. Industrial lasers use a wavelength that gets absorbed well by most materials, and they pulse their beam hundreds to thousands of times per second in short, extremely-high-intensity bursts. It's the equivalent of delivering short, hard punches instead of a long, weak push. For example, Jackie Chan is going to have a better chance of breaking a board than a small army of four year old children pushing against the same board. There's also the issue that heat doesn't have time to dissipate during the short pulse of an industrial laser.

Depending on the application, you might also look into using laser diodes: there are varieties with small packages, simple drive electronics, low-to-mid power, different colors, and a few that are only a couple bucks. You'll still need your own optics to use most of those, though. A more expensive high-power laser diode can burn through some materials, like paper, if focused and left for long enough. Those will have a dangerously large current draw, so please be careful with your electrons.

I don't think its possible cause beams such as lasers are not just light but light that is amplified by radiation

kelseymh6 years ago
No. A laser beam is not just focused. It is both naturally collimated (by the lasing process) and it is also coherent (it acts like a single wave, not a collection of overlapping waves). An LED is not a laser diode.

There are simulated "laser pointers" which use mechanical collimation and focusing of a cheap LED, but you don't get either laser properties nor any sort of intensity as a result.
DIY Emilio (author)  kelseymh6 years ago
I know all of that. I want to know if through optics you can form a beam from LEDs that is laser-like, not as accurate and coherent as a laser.
What do you mean by "laser-like"? The definition of a laser beam is coherence. If you don't want coherent, then just a collimator and lenses.
DIY Emilio (author)  kelseymh6 years ago
Just a beam that is focussed down so much that its beam is similar to that of a laser's. I was thinking of using a collimator, parabolic dish and double concave lens to do this, but I'm not sure if it's the best way.
Well, you can get an approximation: if you put the LED at the focus of a good quality small parabolic dish, then you can a roughly collimated beam out (that's just the inverse of the freshman optics focussing problem). Once you've got a parallel beam, then you can use a pair of lenses, one convex and the next concave, to make the collimated beam narrower.

But you are not going to get anything like a "burning laser" out of this. The power output in light of an LED is miniscule, as conservation of energy can tell you.

i have a 50 watt LED, even if only 5% of the light energy was directed onto a 0 degree beam with a beam width of 1mm that would be more than enough to burn. i'm interested in this because i want to use 2 of these 50 watt LED's with a 10 degree beam to replace my 200 watt incandescent head lights and with the simple lenses i have on hand i cant get the beam under 100 degrees, and the specialty LED lights i bought only go down to 35 degrees, they are bright as all get out but light up the tree tops but the light does not go nearly as far out as my traditional headlights

graham6413 years ago

I have used a junk 4 inch diameter double convex lens and at 30 feet the LED would focus as narrow as a laser pointer. I need the same ability now but with a lens approximately the same diameter as the LED

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lux_manish5 years ago
Hi,Till now ,I think 7degree beam angle is possible.
rickharris6 years ago
An ordinary LED - No, on all counts. HOWEVER of course most lasers you will come across are generated by a special LASER Diode, a sort of super LED.

You can focus the LED light into a spot with a good reflector or lens. You can make it look like a beam by using it to light up an acrylic rod, but not make it satisfactory burn.

(Some high power infra red LEDs may be powerful enough to pop a coloured balloon but not at any distance.)
DIY Emilio (author)  rickharris6 years ago
I'm not talking about a beam just as coherent and direct as a laser diode. Just light focussed from LEDs to form a beam that could possibly burn an object.
Calculate the power output of an LED (you can look up that information). Then calculate the power needed to burn something (you can look up that information). Compare the two.
DIY Emilio (author)  kelseymh6 years ago
That would be a pretty difficult one to calculate since so many variables would be present in the calculation: wavelength, a given affected area, refraction in air, output power, atmospheric absorption, output angle, distance from subject, and probably a bunch of other things. I figure that a laser with a 1 mm diameter dot and 150 mw of output power will burn some objects around a 530 nm wavelength. With an led of 1.5 watts you should then be able to burn an object if you can manage to focus most of its light down to a 1 cm diameter, and any more focus should burn even more. I know that a diameter of lower than one centimeter is possible, but lower diameters would probably require more precise and complicated optics (something that I'm afraid to attempt because of cost).
It's power per area, not power per diameter, that's the issue. If you're just using the same power output (assuming 100% conversion of the power consumption to light), then the diameter goes like the square root -- 150 mW on a 1mm diameter dot is equivalent to 1.5 watts on a 3.16 mm diameter dot (sqrt(10)).