collimation lens for fiber laser

[Larsen]

Hi

I have a Coherent FAP 800 808nm fiber-laser which I intend to use for cutting and 523nm application. When i first bought it I thought that this laser should be fairly easy to collimate, but I was wrong. I now use a 1mm 0.55 NA fiber, but I intend to get a better one for a better beam profile.

So my first question is. Where do I get 0.8 mm fiber with 0.35 NA A.R. coated for a reasonable price?

And my second question is: What kind of lens will be recommended for focusing the beam for cutting appliances and a 5mm diameter ND:YAG crystal?

[bwang]

AFAIK FC diodes cannot be used for machining/cutting.
DO NOT try to change the fiber on the diode. It's impossible to realign without a 3-axis micropositioner and a power meter.
These diodes are usually used to end-pump Nd:YVO4 crystals, to generate 1064/532 nm light.

[Larsen]

AFAIK FC diodes cannot be used for machining/cutting.
DO NOT try to change the fiber on the diode. It's impossible to realign without a 3-axis micropositioner and a power meter.
These diodes are usually used to end-pump Nd:YVO4 crystals, to generate 1064/532 nm light.

http://www.youtube.com/watch?v=bARlFw1TgpM

As you can see it is possible, but the beam diverges quickly. I tried charging a nd:YVO4 crystal with ktp glued on. It made an insane green beam before cracking shortly after.

My concern here is what lens and fiber i should select to reduce divergence and focus it to both cutting application and to pump Nd:YVO4 crystals.

[bwang]

There are good reasons why commercial cutters don't use diodes. 40W of 808nm in a beam like that won't cut much - acrylics will transmit it, and it's not nearly enough to cut metal. The output of a FAP is a vaguely beam-shaped blotch with 15 degree divergence in a 800um spot. At the expense of divergence, you can decrease the spot size, and vice versa.
Building an end-pumped Nd:YVO4 laser with it is a lot more reasonable, considering that was its original use. Focus it onto the vanadate with the appropriate optics - I'm sure Koechner's "Solid State Laser Engineering" has something to say about it. I'll go check for you later.
For big green, you'll want an L-fold cavity.
Also, make sure your KTP/LBO/whatever is (1) properly phase-matched for the 1064->532 conversion and (2) appropriately AR coated and/or brewster cut.

[Larsen]

I was thinking of running a short plan mirror cavity mounted on precision mirror mounts. is that and hopeless idea?