25 dollars via PP to who ever best answers this optical problem.

[Laser57]

OK, who can give me some solid optical information regarding laser lines? How can I make a laser line with the least amount of divergence in the plane opposite of the line? If I think your answer is best, after two weeks I will choose who won and send the money via PayPal. When I take this question to Edmund Optics they don't have a clue.

Chris

[mixedgas]

Its real simple. You start with a ultra low divergence, TEM00 mode laser such as a HENE. What you get is ALWAYS is a constant product of the laser cavity's initial output beam diameter and initial divergence. If you have a high divergence laser, the only way you can decrease the divergence at the target is to increase the beam diameter. Generally the longer the laser cavity, the lower the divergence, as well.

So if I have a three milli-radian beam, and I upcollimate it by a factor of ten, I get a 0.3 mR beam. If I have a 10 mm diameter 5 mR beam, and I downcollimate it 2X using a telescope, I now have a 5 mm diameter 10 mR beam. Its always a constant product of the initial diameter and divergence. For a given beam, the diameter x divergence product is ALWAYS a constant. This is due to the law of conservation of energy. The concept is called Etendue...

Generally, with a given laser, the only way you can decrease divergence is to upcollimate.

How you produce a uniform line is another discussion, but if you ARE using the proper line optics, they should have little to no effect on the un-expanded axis of the line.

While some in some very rare times you can mask off bad transverse modes in a beam from a really imperfect, non-Gaussian, diode laser, and use the less divergent central core, you will always loose energy in the process. If a laser is well made and already has an initial low divergence, no amount of masking will help you. This masking is generally best done using a Spatial Filter. Masking only applies to very high power diodes with very large chips... Masking is used if your beam is a series of huge blotches.

How you do this all depends on what size beam diameter you want at your target and what the parameters of your laser source is. It is a very broad question without specifications on what your real world application is.m

It is all about the quality of the initial source.

Things you need to search for and read:
Transverse mode
Longitudinal mode
Gaussian Beam
Multimode Beam

You CAN upcollimate or downcollimate in one axis using cylindrical lenses, which if used properly, only have an effect on one axis.



Steve

[planters]

Steve is right and so that's that.

But...even though I think I know what you mean and Steve's advise is sound, you did not specify the propagation conditions completely and so there are some interesting, if challenging, approaches. A Bessel beam is an optical phenomenon where interference acts to produce a non-spherical wavefront. At the expense of power loss the beam can propagate with little divergence. The far field will not be any brighter, but the divergence can be lower. This can be produced with an axicon lens set up. Or, you can do what only the very highest power lasers can accomplish and that is to create a self focusing channel in the atmosphere by allowing the intense beam to heat and air which for a brief instant acts as a lens to counter the divergence of the propagating beam. However,an audience might not appreciate this very much.

[Eidetic]

I'm still trying to figure out what is meant by "the plane opposite of the line".

[swamidog]

I'm still trying to figure out what is meant by "the plane opposite of the line".

i assumed it meant perpendicular, but (shrugs).

[kecked]

There is one way I think you can violate this law. Using one laser to pump another laser as the new beam is the result of the new lasers cavity and not the pump.

For example a ruby laser takes a flash lamp with divergence as high as possible to make a laser beam. Not sure this really counts as an example as you are really just using the energy of the pump and not the properties of the pump laser beam.

[buffo]

To me it sounds like he wants a laser line generator like you'd have on a compound-miter chop-saw: something to denote where the cut will fall. And if it is, in fact, for a saw application of some type, then it would follow that he needs a narrow width beam because the saw blade has a narrow kerf.

Either way, this is a solved problem. As Steve said, starting with a low-divergent laser source is the key. Beyond that, generating the line is trivial. Diffraction grating, cylindrical lens, or spinning mirror; any of the three will work and won't affect the divergence of the opposite (perpendicular) axis.

As an aside, I'm certain that Edmund's Optics sells several solutions to this problem. I think the reason they weren't able to help is due to the awkward phrasing of the initial request. Had he asked for a line-generating diffraction grating or a high-index cylindrical lens they would have known exactly what was required.

Adam

[White-Light]

I'm guessing these are what you're looking for combined with a laser as described above:

http://www.edmundoptics.com/optics/optical-lenses/cylinder-lenses/laser-line-generator-lenses/1910/

http://www.laserlineoptics.com/powell_primer.html

[Eidetic]

The Powell lens looks great. I was thinking an anamorphic prism pair, used backwards with a small bore he-ne to make the line thin, then scan or otherwise expand the other direction to make the line.

[Laserman532]

a bore diameter of one photon with a cavity length of infinity using only the thickness of the reflective coatings as your mirrors in the vacuum of space...but then again...i could be wrong...