MORE help Collimating a multi-mode red diode

I know I all ready have a thread started about this but I am starting a new one since all that info in the other one is old.

Here is what I think I know so far, I would like a few extra opinions before I go any further with this. I have a TO-3 diode with an FAC so I don't need a cylindrical lens to help collimate the beam since the FAC is doing what the cylindrical lens would do.

I bought a TO-3 housing that mounts the diode and a lens assembly. The lens assembly seems to be an aspherical lens with a cylindrical one after it. So I can't use this assembly as it is designed for a diode without an FAC, correct? When I try and collimate the beam with it the best I can get is a large square about 1"x1" at 6ft. So my next step would be to make a new lens holder and use a regular lens like the one from LarryDFW coated AR for red?

I have a pic that sucks cause it is from an Iphone. The pic is of the diode output with no lens.

Yes, you should be able to collimate that fairly well with just a convex lens, at least I think that's what you're asking...

I have some 16mm glass lenses coated for 808. They give good transmission for red too. With these I can get an 1/8" square at 6' from a 2W 808nm diode with FAC. It should give similar results with red.
The only thing is, the beam diameter at aperture will be quite large compared to what you get with a short focal length aspheric... although divergence will be better and the larger lens will collect more of the light. If you've got more than a watt or two, burning will be easy even with a fat beam.
I may not be using all of them so if you are interested, I can let you know if I have spares in a couple weeks.

Yeah... you seems to have the beam defined...
all you need to do now is collimate it... IMO

Jerry

The easiest way to use it is this:

First collimate to the sharpest LINE you can get with a short FL collimation lens, Next use a +Fl cylinder lens to get the best beam spot, If you do it right you will get a dot that is similar to a raw hene laser in divergence...

OR...

Use a -FL cylinder lens and a short fl collimator lens to get a rapidly diverging square dot then collimate with a medium fl (3-5 inch) lens What you get is big 1/2 inch dia beam, but divergence on par with the very best dpss laser pointers.

OR..

IF you have a diode with an integral FAC, then all you need is a short FL aspheric lens to collimate the dot to a quality between these two.

MISTERWILLING;

All you need after the FAC is a collimating lens to focus the beam.

Try the TO-3 lens assembly wo the cylindrical lens.

Then, compare it to one of my Hi-Power lens assemblies @ ~ 2mm.

The open aperture must be large enough to collect all of your Red beam, at the focus point.

I also have some 25mm diameter plano-convex lens assemblies with a 5/8" FL,
that another LPF member (sbdwag) is trying on his 5 watt IR diode:


LarryDFW

Okay seems I'm going in the right direction, I just didn't want to machine a housing if I didn't need to. This diode is bright! I don't know any exact details but I know it is close to 635 because it is soo much brighter than my LPC's at about the same burning power. Now I just have to get the beam down to ~3mm for use in my scanner application. Thanks for help guys.

Back again! Okay I machined a custom housing and mounted a 405-g-1 lens directly in front of the diode and all I could get was a 5 inch by 2 inch rectangle (120mm x 50mm) at 6ft. Moving the lens any further away only un-focuses the beam further. Larry I may have to try one of those larger lenses you have. This is going into a laser projector so a larger lens and longer focal length don't bother me, I just need to get this beam tight.

MISTERWILLING;

I have them and other lenses available.

Just give me a call.

LarryDFW

MISTERWILLING said:

Back again! Okay I machined a custom housing and mounted a 405-g-1 lens directly in front of the diode and all I could get was a 5 inch by 2 inch rectangle (120mm x 50mm) at 6ft. Moving the lens any further away only un-focuses the beam further. Larry I may have to try one of those larger lenses you have. This is going into a laser projector so a larger lens and longer focal length don't bother me, I just need to get this beam tight.

Click to expand...

Just curious, but why are you using a 405nm lens?

Also, (this might be a stupid question, but I'll ask anyway) are you sure that the housig is the proper length to place the lens where the best collimation point will be? If it is machined with the lens mount too close or too far away, then the adjustments you make can't move it far enough to collimate.. Just a thought

Its just a lens I had available and it is coated to allow red through as well, just optimized for 405. I was going to replace it with a lens that is of the same shape but coated for red which Larry has available if it worked.

I had the lens able to move from a distance of 1 inches to 0.001 inch, it was focusing the rectangle closer and closer as I went it but never focused it enough.

I will contact you Larry, my cell Phone broke so it may be a couple of days before I get a new one.

If the TO-3 has an integral FAC lens, then you can use any normal aspheric lens to collimate it, The one out of an old flatbed scanner works nicely.