help with optics and lasers

[Kenom]

Ok I'm clueless when it comes to optics. Theres a whole level of math that just goes beyond what I'm capable of doing. anyway, I need help here as this project is going to go beyond what I'm capable of doing myself.

here's the scoop: I've got 4 40 Watt Fiber coupled 808nm laser diodes to play with. The fiber that I've got on these badboys is SMA fiber. Now I've not the funds to purchase a SMA fiber collimator from thorlabs or edmund optics. so I am utilizing some errrr mickey mouse engineering.

Ok so this is a SMA to N adapter used for wireless stuff. Not a clue exactly what for or do I really care. It's going to serve my needs. I'm in the process of trying to find a lens that will fit into this sucker at 8.25mm ID. Anyone know where I can find one. This fits right onto the end of my fiber optic cable so I know it will work if I can find the optics for it.

 

[steve001]

I'm certain Edmund Optics has a lens to fit. Did you know Edmund has a forum for asking questions ?

 

[ElektroFreak]

For maximum efficiency, you'll want to know what focal length the lens needs to be. Personally, that's all i can tell you. I'm clueless when it comes to figuring that kind of stuff out, but I'm sure someone else on here can..

 

[Kenom]

I'm certain Edmund Optics has a lens to fit. Did you know Edmund has a forum for asking questions ?

Ok what about "edmund optics and thorlabs are too expensive" is unclear? why I've looked there already and am not going to pay $75 for one lens. focal length is irrelevant as it will be adjusted in or out of the chamber to change the focus to where I want it. I just need the OD of the lens to be 8-8.3mm

 

[suiraM]

Get an 8mmØ ball lens.

Crown glass is cheap. Flint glass gives shorter focal lengths, but will probably cost more. The focal spot will be long, meaning along the optic axis, due to the aberration and multimode in, but that's a good thing if you're dumping 40W into a crystal (you are dumping it into a crystal, right?)

Also, Surplus Shed has a lens finder which you can use to find a plano-convex or double-convex lens with the right diameter, if you're not happy with a ball lens.

HTH.

Edited to add: Of course the focal length matters. If the fiber output diverges beyond the aperture of your lens in a shorter distance than the focal length, then you cannot collimate all the light. And the divergence depends on how short the focal length is, as well. For a tight beam, you want a half-ball lens that can be glued directly to the fiber, but that takes math, so a gradient index lens is the second best choice, but that takes money or shipping time, leaving you with a short back focal length PCX or DCX lens or a full ball lens, all three of which can be fiddled with to find a proper focus. Just make sure that adapter will center the fiber well- one would normally use a ferrule for a thing like that.

 

[LarryDFW]

Kenom;

I just looked thru my various laser diode lens collection.

I do have a AR coated plano-convex glass lens that is close.

Forty watts may be pushing the limits for the AR coating, but the glass should handle it fine.

It is 7.6mm in diameter. A slight crimp of the ferrule should be all you need to mount it.

The Focal Length is fairly short @ 8 mm.

I have $5 in it. You're welcome to it at that.

Is the final application etching ?

LarryDFW

 

[steve001]

Ok what about "edmund optics and thorlabs are too expensive" is unclear? why I've looked there already and am not going to pay $75 for one lens. focal length is irrelevant as it will be adjusted in or out of the chamber to change the focus to where I want it. I just need the OD of the lens to be 8-8.3mm

Like the other posters said focus is relevant. You also have to consider thermal properties that a lens can handle. 40W into an area of at most 52.16sq.mm might just cause damage to a lens