LED-Based laser idea

Hey,

Would it be possible to take a really powerful LED and put it through some kind of filter that only lets through 1nm of the spectrum? Then you would only get coherent light and be able to make this into a laser, right? Or does a filter like this not exist?

-Jakob

pianoman2011 said:

Hey,

Would it be possible to take a really powerful LED and put it through some kind of filter that only lets through 1nm of the spectrum? Then you would only get coherent light and be able to make this into a laser, right? Or does a filter like this not exist?

-Jakob

Click to expand...

The closest dichroic filters I've seen reflected 635nm and passed 650 to combine red lasers in a show system. Not saying it isn't possible but if it is it would be quite expensive. Plus then you cut like 95% of the output out of the LED.

Would it work if your conditions were met? I'm not really sure but it certainly wouldn't be efficient.

The closest dichroic filters I've seen reflected 635nm and passed 650 to combine red lasers in a show system. Not saying it isn't possible but if it is it would be quite expensive. Plus then you cut like 95% of the output out of the LED.

Would it work if your conditions were met? I'm not really sure but it certainly wouldn't be efficient.

Click to expand...

About inefficiency, I wasn't thinking about red. I was thinking about yellow or blue or something that already has very low efficiency in a DPSS unit... red or violet would be pointless to do it with since those colors are so much easier to make.

-Jakob

from what i know the nm designation doesn't make light coherent or not. and if you could filter a source of light to 1nm (this is a question now), wouldn't it be cancerous, like an x-ray or gamma ray. I couldn't find a table to show.

You will get monochromatic light, but not coherent-monochromatic light.

from what i know the nm designation doesn't make light coherent or not. and if you could filter a source of light to 1nm (this is a question now), wouldn't it be cancerous, like an x-ray or gamma ray. I couldn't find a table to show.

Click to expand...

Woah, what makes light coherent then. And I didn't know that would make it cancerous! How would it do that?!

-Jakob

You will get monochromatic light, but not coherent-monochromatic light.

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Whats the difference b/t the two?

Coherent light makes a laser. Monochromatic light is just one (1) colour.

Coherent light is electromagnetic radiation (or photons) that has a uniform wavelength and phase. and monochromatic is light with just one color like a blu-ray. the two term can coexist but one doesn't make the other. think about this, all brands of fruit loops cereal are CEREAL, but not all cereal is fruit loops. :na:

chipdouglas said:

from what i know the nm designation doesn't make light coherent or not. and if you could filter a source of light to 1nm (this is a question now), wouldn't it be cancerous, like an x-ray or gamma ray. I couldn't find a table to show.

Click to expand...

No. He's talking about bandwidth, you're talking about actual wavelength. It wouldn't be changing the wavelength to 1nm, it would be making the bandwidth 1nm. A la you have a blue LED, and you apply a filter so that only light with a wavelength between 472.5 and 473.5 passes through. Thus, the bandwidth is 1nm, and the light is quite monochromatic.

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As far as coherent vs. monochromatic: Coherent light is monochromatic, but just because light is monochromatic does NOT make it coherent. To be completely honest, even laser diodes are not 100% coherent, or even 100% monochromatic, but they're extremely close to it, and for all real world intents and purposes, are coherent and monochromatic. Coherent means the light is in phase with itself, and all heading in the exact same direction. Think a group of soldiers all in step marching down a road. All in step, all traveling parallel in the same direction. If each soldier is a photon (or each column of soldiers comprises a single continuous wave, so to speak, it's a metaphor, it's not a precise analogy), then the overall effect of them marching together is that they are coherent. This is the output of a laser.

An LED, you can instead think of a group of people starting in one place, and then running out in all different directions. Some people are taking little tiny steps and some people are taking big steps, so they are not in step with one another, even if they are moving the same speed. All the photons are going in different directions, with different wavelengths (ie step lengths), even if they're at the same speed. Remember shorter steps (wavelength) means more steps to get the same speed, which is a higher frequency, so this cool littel metaphor still kinda holds.

So, if you filter that group of people that are spreading out to only the people(photons) that are taking steps of the exact same length, then you get monochromatic light. BUT, those people/photons are all still heading in different directions, so they are NOT coherent.

Pullbangdead pretty much summed it up.

I made a pretty picture if you're still confused.

Yes, I think I did mean bandwidth... I just didn't have the vocabulary to say it .

I finally understand now! I didn't realize that being coherent and being the same wavelength (now, being monochromatic ) were two completely different things. So a laser now has a new demand that I never realized. Thanks everybody for helping me understand the definition of coherence. And I love the picture, pseudolobster! I'm a visual learner so it really helps a lot.

-Jakob

so in retard terms.

this means you cant use an led to make a "laser"

<--------slow.

[obvious]Yeah, I think I got that now.[/obvious]

-Jakob

Hey jakob, I knew this was a familiar topic, but my memory sucks. here is a link from this site that rog8811 found. hope this helps http://laserpointerforums.com/laser_pointer_forums_3/forum/showthread.php?t=38688

Oh yeah, I read about that. Neat way to make a mutant-DPSS-like-thingy. Wasn't it something about pumping vandate-like crystal with an LED?

-Jakob