Optics 101

[Hemlock Mike]

Red Diode lasers have a single optic to focus.

I have a NdYag source and I need to know what lens I need to focus that source like a red diode. I really don't want to use a two lens columnator -- but I may have to . I burned a focusing lens last night :-(

Mike

 

[comozo]

any positive focal length lens will do but the material of the lens is special like zinc selenide. Edmund Industrial Optics is one company that carries lenses for the IR region

 

[Hemlock Mike]

Comozo --

I believe you're correct but what FL ?? The reds need a little tuning to go from 3' to say 20'. It's also got to handle a bunch of watts !!

My DVD reds have focus adjustments but I can't seem to get one of these lenses to work at 1064 nm.

Mike

 

[comozo]

It's not the focal length that is the problem. It sounds like you don't have enough travel distance to focus the beam, back or forth

 

[YAG]

Wrong... zinc selenide lenses are for CO2 lasers at 10600 nm, not 1064nm. You need to get a beam expanding collimator. Nd:YAG lasers have poor divergence usually, and the only way to reduce this is to increase the beam diameter with a newtonian type (typically) beam expanding telescope arrangement. Alternatively you can use a convex lens of x times the focal length of a convex lens to achieve x times beam expansion. Typical collimation expansion is 2-5.

 

[comozo]

Wrong... zinc selenide lenses are for CO2 lasers at 10600 nm, not 1064nm. You need to get a beam expanding collimator. Nd:YAG lasers have poor divergence usually, and the only way to reduce this is to increase the beam diameter with a newtonian type (typically) beam expanding telescope arrangement. Alternatively you can use a convex lens of x times the focal length of a convex lens to achieve x times beam expansion. Typical collimation expansion is 2-5.

I don't take it HM wants to collimate the beam just focus it. A positive lens placed in the beams path will do just that the same as a magnifying lens does for the Sun.
If by poor divergence you mean a high divergence rate then a single lens may be all that's needed. If HM needs a small spot size then a two lens system is what he may want. I do believe zinc selenide lenses can be used for that wave length. After doing a bit more research it seems BK7 or fused silica will do. Take a look here http://www.newport.com/Singlet-Lens-Tutorial/533081/1033/catalog.aspx

 

[Hemlock Mike]

Lots of info here. The ZnSe lenses I have are indeed made for my CO2 laser which is way below 1064 nm. They have a very yellow color and most likely tuned to that deep red.

The columnators I made for my old NdYag are kinda big clumsy things with the expander lens and a focusing lens. I was hoping for a lens system similar to a red diode which is a single optic going from say 3' to 20' with a minimal ajustment. I'm trying to keep this small.

Glad to see people here with knowledge and good ideas. That's why we come here.

Thanks to all of you.

Mike

 

[Hemlock Mike]

About 20 years ago, I built 2 columinators for my old yag. I had a book from Edmunds and I used that to make two -- one about 5X and one about 10X.

I can't find my designs or the book now. Maybe you can help. I need to get a -FL lens and a +FL lens to fit into about a 2" tube. All I want is to POP one at about 20'. I sure won't be bringing anything down with this !!!

Formulas etc will help here.

Mike