half the divergence with 2 mirrors ???

[highvolt]

Hi,

I just came across something on laserfreak.net. The text is french and german, but it's basically the images that are the most interesting.
I know that it's impossible with a lens to get better beamspecs. (divergence x beamdiameter = constant like behaviour).
But how about a mirror ?
http://www.laserfreak.net/forum/view...&highlight=635
similar approuch:
http://www.laserfreak.net/forum/view...=118859#118859

Can this work? Or is this whole thing l like the perpetuum mobile discussion: thousands of people try to build one while we know it can't physically be done

Anyway, by the looks of the drawing, it sure seems plausible.

[bulldog_99_00]

I don't have much experience with optics yet, but I read french and german. So, a summary:

I believe you understand, but I'll attempt to explain to anyone who's interested: What you're basically doing is splitting a beam in two along it's centerline and folding the divergence of one half onto the other. (You actually do this once horizontally, and once vertically). That way, you have half the divergence (the drawing explains that well).



The french concensus is: seems like a plausible idea, but will it work in practice?

The german concensus is: seems like a plausible idea, but only if you have a fat beam to begin with.

This technique's success seems to depend on the diameter of the beam and the desired focal point. The thing is, the two halves will only be able to overlap perfectly at a single focal point. You overlap the divergences by separating the two halves of the beam and then crossing them at a certain angle. So, the divergence of the beam far from the focal point will be worse than it would've been normally, because you have the normal divergence + the angle you added acting on the beam.

The mirrors at the origin split the beam, right?
Scenario #1) Big beam, big divergence (the original context). At small distances, this technique seems like it would work.
Scenario #2) If the beam is moderately thin, or you're focusing the beam moderately far, the split at the origin will make the beam look either very fat, or make the beam look like multiple distinct beams.

[mixedgas]

The french concensus is: seems like a plausible idea, but will it work in practice?

The german concensus is: seems like a plausible idea, but only if you have a fat beam to begin with.

Steves concensus, unless you have a huge pretty much incoherent beam, knife edge diffraction at the spliiting point from the edge of the mirror will ruin your day. Anamorphic compressors rely on a index of refraction bend, mirrors dont. A thing called etendue, timed to the laws of thermodynamics, haunts mirror based beam compression. So yes this only works at one focal point, and even then its lossy.

Steve