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A question about optics

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Apr 2, 2020
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Hey all, hope everyone is healthy and safe right now.

Folks, I have found my way into the bourbon reserves after a long lab day so I have a question that I'd like to farm out to you all - it has to do with optics and beam combination. I'm a molecular virologist and not a physicist, so I'm out of my depth there.

I understand that focusing lenses image not only the incident light, but the spaces between, hence a focal point of a lens being not purely a combination of beams. That said, the divergence of the beams after that focal point is known, and I suppose I'm wondering what would happen if one were to put a small collimation lens *close* (but not touching) the focal point of a biconvex lens. By sampling the virtual image taken some small distance d from the focal point, would the collimating lens be able to create a beam that, despite not being a true combination of beams, would have a higher energy density with the desirable low divergence, low(er) beam size properties of a primary beam?

I've attached a hopelessly simplistic illustrator diagram (please be merciful, all of my illustrator presets and skills are for modeling cells and viruses, this straight line stuff is novel!). Frankly the diagram is there mainly in case my words are somehow unclear about the setup I'm describing because I know about the 1000 ways it's inaccurate thank you :p) I welcome all input here but especially from those who can explain the physics of this - I work mainly with fiber lasers with integrated optics packages rather than on optical tables so I'd love a better understanding of the processes underway!





Cheers Lens array.jpg

LM
 



kecked

Active member
Joined
Jun 18, 2012
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494
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You might try this first. Stack the beams with mirrors to make it as tight as you can than use a pbs cube to combine. Not shown is a waveplate to turn the polarization of one of the stacks. Now you start with a much more compact beam. Might be less than 1-2cm with 24 beams. So it would be a cross of 12 stacked beams. After that your choice is a fatter better divergence beam or a thinner more divergent beam. I think the company arctos does this for their high power red.

the method is called edge combining. The image is not mine. So from your drawing you have multiple rows. Do this for each two rows and edge combine the results. You can’t use the pbs trick more than once Per set of rows or at the end as shown below.
if all you want to do is burn something then your idea is fine but it will only work at a fixed focal distance.
see styropyro videos.
A9541228-E743-4031-8BAC-FE6DAA9CAAE8.png
 
Last edited:

Cyparagon

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Sep 12, 2007
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Your illustration (OP) describes a beam reducer. The opposite of the much touted beam expander. A law of optics we're quite familiar with here is: all else equal, beam divergence is inversely proportional to beam diameter. This is derived from the laws of diffraction, which are in turn derived from quantum effects.

e.g. if you halve the beam diameter, you roughly double the divergence. There's no way around this. Physics says no.
 
Joined
Apr 2, 2020
Messages
39
Points
18
Your illustration (OP) describes a beam reducer. The opposite of the much touted beam expander. A law of optics we're quite familiar with here is: all else equal, beam divergence is inversely proportional to beam diameter. This is derived from the laws of diffraction, which are in turn derived from quantum effects.

e.g. if you halve the beam diameter, you roughly double the divergence. There's no way around this. Physics says no.
Physics is a harsh mistress - I think I misspoke in the post (and definitely could have drawn the diagram better since it resembles a ray diagram which isn't exactly what I was going for) - I know about the unfortunate physics of beam diameter/divergence, I was more looking at a way to bring multiple different beams in an array closer together rather than reduce the diameter of any individual beam. Sadly, as you described, that's an inevitable effect of this technique. Time to figure out how to design some kind of custom knife edger...thanks for the info!
 




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