Collimating multi-mode diodes to a tight beam using Biconcave Lens

[loreadarkshade]

I was wondering how possible this would be. I have thought about it for a while now but have no way of executing this.

Has anyone ever messed around with lenses like this to collimate the laser even further?
I don't know much about optics, but isn't this how the beam expander works?

Why hasn't this been done before?

 

[RedCowboy]

You mean like a telescopic reduction ?
For one thing the coherence length of the multi mode diodes is very poor, so your reduced diameter beam or beams will diverge quickly.

Here I did that with a ring of beams from m-140 diodes, but the beam bundle spread out pretty quickly as did the beams after the biconcave.

The problem with the multi mode blues is the unequal divergence, the fast axis is very aggressive and needs to be corrected via. cylindrical lens pair, that will give you the beam you want or much closer to it.

 

[paul1598419]

Biconcave lenses are used primarily to expand a beam in DPSS lasers before collimating the beam. I haven't heard of them used just for focusing, or collimating the beam, in a direct diode laser.

 

[kecked]

Still an interesting thought and thanks for sharing. It might be effective using the fac corrected diodes but just for a single diode and then with a collimation lens after it for actual focus. I’d expect a simple telescope to be do the same job with less lens. Some day someone will make some holographic thing to fix the beams based on the pattern for each diode. I’ll be long dead.