Beam correcting optics

As I'm not really sure how to start this thread off, I'll just post my question right away.

Is anyone willing to explain me how exactly I can correct the beam divergence and possibly splash around the dot of multimode lasers?

I've been for answers on the forums lately, but I can't find much more than a couple half-answered questions. I know it is possible to correct some of the beam divergence using prisms, but as you probably know, it's not the easiest thing to fit that in a handheld. Another thing that I came across is putting a small piece of glass fiber in front the lens, but that doesn't sound very viable either.

There are probably other things that I forgot to mention, but you get my point. My goal is to achieve somewhat of a decent divergence with possibly reducing the splash around the dot, all in a handheld device.


I'd really appreciate any advice on this subject, thanks.

Don't drive your self crazy if you don't have a real purpose for needing a corrected beam.

I've never pulled out a multimode and had somebody say "hey is that a multimode with horrible beam characteristics"

it's like if you cook a meal and mess up a little. everybody will think the meal is great unless you announce your mistake. you know what I mean.

Michael.

I get your point, but I would for once love to have a high powered multimode have a decent divergence and rather clean dot. Even if I end up not correcting a laser's beam, I'd still like to know how it's done, just like I wanted to know how DPSS lasers worked when I first signed up here.

gozert said:

I get your point, but I would for once love to have a high powered multimode have a decent divergence and rather clean dot. Even if I end up not correcting a laser's beam, I'd still like to know how it's done, just like I wanted to know how DPSS lasers worked when I first signed up here.

Click to expand...

There are a multitude of different methods.

Prism pairs, cylinder pair, fiber coupling, spatial filtering, FAC lenses, beam expanders etc. Some methods work better than others depending on how the beam starts off, how much power you are willing to lose and what kind of beam quality you want at the end.

A lot of these methods are generally used to fix a higher divergence on one axis, as is seen with many high powered diode lasers. The Prism Pair, Cylinder Pair and FAC lens for example are generally used for this. Spatial filtering will clean up artifacts around the beam rather well. Fiber coupling will make square multimode beams gaussian again, or at least much closer to a true gaussian beam.

gozert said:

I'd still like to know how it's done, just like I wanted to know how its done

Click to expand...

You got me there!! That I can get behind =)

Michael.

diachi said:

There are a multitude of different methods.

Prism pairs, cylinder pair, fiber coupling, spatial filtering, FAC lenses, beam expanders etc. Some methods work better than others depending on how the beam starts off, how much power you are willing to lose and what kind of beam quality you want at the end.

A lot of these methods are generally used to fix a higher divergence on one axis, as is seen with many high powered diode lasers. The Prism Pair, Cylinder Pair and FAC lens for example are generally used for this. Spatial filtering will clean up artifacts around the beam rather well. Fiber coupling will make square multimode beams gaussian again, or at least much closer to a true gaussian beam.

Click to expand...

I read about fiber coupling being a relatively hard process due to me having to place a piece of glass fiber precisely infront of the lens. Although I of course don't have any experience doing this, it does sounds like a pain to do.

For spatial filtering, it definitely sounds viable, but the prices on these things are outrageous for what I've seen. Also, a spatial filter fit in a handheld? I saw a couple at Thorlabs that looked like they were being used for lab lasers rather than handhelds.

And the prism pair, I read in a thread made by Cyparagon a while back that using prisms decreases output by a rather large percentage. Does this differ for each wavelength, or is it the same overall?

Edit: I just read about a cylindrical lens. Is this as "simple" as it sounds, or is this another very complex thing?

Anyone willing to help me out some more? I saw a few possible solutions, but I have no clue as to what's available to be put in handhelds.

gozert said:

Anyone willing to help me out some more? I saw a few possible solutions, but I have no clue as to what's available to be put in handhelds.

Click to expand...

Do a search for some of my builds...listed in the sig below. Forget FAC and Fiber Optic coupling ...way outa our price range....and besides....the Anamorphic prism's and Cylindrical lenses do a good job to correct the multimode diode.
Putting optics in hand helds is my thing !! Specifically corrective/adaptive optics. There are several members on LPF who also do this. It can be done !!It has been done and it will continue to be accomplished.

There is one main stumbling block...how does one position the optics to accomplish correction in a hand held format. I suggest you review the build thread.... " Sky Blue Ramjet " in the Experimental area. This will serve as a primer for your understanding.....not the theory of how the optics work....which is interesting....But...How is it done !!!:eg::eg::eg:

Thanks guys. I have some ideas on how to properly correct beams now. I'm not yet completely sure about how exactly spatial filters work, but I'll find it out some day. I'll be starting a 2-3 diode build soon depending on how much heat I can manage to dissipate from the diodes. The info I got from you guys will definitely be useful for what I'm trying to do.