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05-29-2008, 02:38 PM #1
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n-sane
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Half mirrored prisms & multiple lasers questions

Hey guys,

I'm making a small diy dvd laser burner for my physics project, but i'm pretty big into diy electronics and like to funk around, so here's my idea:

Using several half-silvered prisms such as the ones found in the very dvd drives that probably everyone reading this has at some point ripped apart, can one connect in series several simple 200mW-in-an-aixiz-case-burners such that the beams converge into one with the use of several previously mentioned prisms in line?

I understand the resultant beam will lose its coherency because of the several sources, but nonetheless the resultant intensity of the beam should still equal the sum of the source beams? So 5 200mWers in such an arrangement should produce the burning power of a single 1W ?

Please let me know if this is remotely possible or a complete flop (which i assume it should be since i haven't seen it used yet).

If this could work indeed, i've several cd drives i'd rip apart for the prisms, and i'd order 5 aixiz lasers + 5 200mw diodes off them to use in this project.

Cheers guys!

05-29-2008, 02:49 PM #2
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GooeyGus
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Re: Half mirrored prisms & multiple lasers questio

Yup this is possible! The biggest issue will obviously be alignment, and you will lose a bit of power in the combining optics. Good luck!

05-29-2008, 03:00 PM #3
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Switch
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Re: Half mirrored prisms & multiple lasers questio

Yeah, it's remotely possible. Remotely as in &quot;you will only be able to combine 2 beams&quot;. You see the prisms use polarization to combine beams of the same wavelength.For example , the prism reflects an X axis polarized beam and passes a Y axis polarized one.This way you can combine the 2 beams, but the result will be a beam composed of the 2.It's pretty obvious why you can't combine this new beam with another. :

05-29-2008, 03:12 PM #4
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Cyparagon
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Re: Half mirrored prisms & multiple lasers questio

As said above: It's tricky, but you might be able to get 400mW.
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05-29-2008, 03:20 PM #5
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FrothyChimp
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Re: Half mirrored prisms & multiple lasers questio

Read up on constructive and destructive interference and standing waves. I'm sure if you do something like that your physics instructor is going to ask you why you don't get 1W from 5 200mW. I would. It will also give you some background on how to tune the combination for maximum output.
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05-29-2008, 06:16 PM #6
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n-sane
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Re: Half mirrored prisms & multiple lasers questio

Wow good reaction to posts on this forum...

Anyhows, several things;

Destructive interference would indeed be a bitch if the diodes were driven by separate circuits, however since they will be driven together from one line, both should technically turn on at the same time producing light that is in phase?
if not, then some fine mechanical distance control would fix the problem. VERY fine mechanical control.

Standing waves only form when the wave is reflected back, ie in air columns though, no? Perfectly timed alternating destructive and constructive interference is created such that the wave takes on permanent nodes at 1/4lambda, 3/4 lambda and so on in +1/2lambda patterns, while crests and troughs of the wave alternate each cycle, no?

And concerning the prisms, must the prism be polarized? Lets say scrap the dvd/cd prisms, would an unpolarized one be so hard to find?

This would indeed be an interesting, modular and above all extremely cost effective alternative to \$1000 1w laser assemblies... 5x\$15 + \$30 or so in prisms and materials !&gt; \$1000+...

Thanks a bunch for the informative replies, please keep them coming!

+++ Now that i think about it, the alignment would indeed be a royal pita.. a challenge even for industry i bet.

05-30-2008, 02:14 AM #7
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bobobob121
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Re: Half mirrored prisms & multiple lasers questio

well you would have much more chance of burning something &quot;that is what i presume your doing&quot; if you just converged all the lasers at one point instead of keeping them all in one straight line. like this....

there might be a formula to find out the total mWage, but i just made this to show what i mean about pointing all the lasers at one point
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05-30-2008, 10:09 AM #8
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n-sane
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Re: Half mirrored prisms & multiple lasers questio

Point of the whole thing would've been to have an actual laser with an infinite focal point instead of focusing the beams every time...
But nice diagram

05-30-2008, 10:18 AM #9
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GooeyGus
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Re: Half mirrored prisms & multiple lasers questio

Quote:
 Originally Posted by bobobob121 well you would have much more chance of burning something "that is what i presume your doing" if you just converged all the lasers at one point instead of keeping them all in one straight line. *like this.... there might be a formula to find out the total mWage, but i just made this to show what i mean about pointing all the lasers at one point

If your drawing is to scale, those are either really tiny lasers or thats a really big match ;D

05-30-2008, 11:18 AM #10
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VillageIdiot
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Re: Half mirrored prisms & multiple lasers questio

That's nothing.

I was trying to get Frothy to fire up all his lazors into one spot for the hell of it but he's probably too sensible or something like that.
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05-30-2008, 01:38 PM #11
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Re: Half mirrored prisms & multiple lasers questio

He'd blow a breaker.
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05-30-2008, 03:45 PM #12
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styropyro
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Re: Half mirrored prisms & multiple lasers questio

Quote:
 Originally Posted by VillageIdiot That's nothing. I was trying to get Frothy to fire up all his lazors into one spot for the hell of it but he's probably too sensible or something like that.
OT: I was going to post the EXACT same thing after reading Gooey's post. I say we have everybody on LPF come to my place after I build the biggest match ever and we all point our lasers at it.
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05-31-2008, 02:42 PM #13
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n-sane
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Re: Half mirrored prisms & multiple lasers questio

Lets please not go off topic...
And unless you can take 10 amps @ 120v through your lazorz... (thats roughly 1200w or 1.2Kw, and thats if you're already running a shittonne of stuff through the same breaker ) don't worry about your breakers.

05-31-2008, 06:09 PM #14
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Re: Half mirrored prisms & multiple lasers questio

lol, maybe i want 25 T.V's running on one receptacle with a bunch of 3 way splitters : )
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06-01-2008, 12:39 AM #15
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GooeyGus
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Re: Half mirrored prisms & multiple lasers questio

Quote:
 Originally Posted by n-sane Lets please not go off topic... And unless you can take 10 amps @ 120v through your lazorz... (thats roughly 1200w or 1.2Kw, and thats if you're already running a shittonne of stuff through the same breaker ) don't worry about your breakers.
I dont think frothy would have a problem exceeding that with his lasers 8-)

but!!! Back on topic.

Ok, so earlier in the thread, switch posted this:

Quote:
 Yeah, it's remotely possible. Remotely as in "you will only be able to combine 2 beams". You see the prisms use polarization to combine beams of the same wavelength.For example , the prism reflects an X axis polarized beam and passes a Y axis polarized one.This way you can combine the 2 beams, but the result will be a beam composed of the 2.It's pretty obvious why you can't combine this new beam with another. :
My question is, why cant you then combine that beam with another? In theory if everything is aligned perfectly, it should be one beam. So, throw that through another prism with a third beam coming through and you should then have 3 in one beam. Right? I realize it wouldn't be 3 times the power because of significant losses in optics and combining and all that stuff, but I can't see why it wouldn't work. Maybe I'm just overlooking something?

06-01-2008, 01:20 AM #16
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Re: Half mirrored prisms & multiple lasers questio

If we take this combined new beam, polarization-wise, it has an x component of 200 mw and a y component of 200 mw. So far, so good. However, if we try to send this beam through a third polarized prism or reflector, this third reflector will then not pass our 400 mw, it will stop whichever of the two combined beams it's polarization will not pass. Limit of beam combining is stuck at two lasers, assuming that the two lasers are of the same frequency. I'm not aware of any existing coating for optics that would allow light to pass through from one side of the optic, but be reflected if attempting to pass in the opposite direction. (directional mirror?) This is the coating that we would need in order to combine multiple beams of the same frequency.
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