A IR Laser diode focusing and module selection for CSEL Laser pointer

[Mike Gaffer]

TL;DR Summary

Building an IR pointing laser - need help selecting a CSEL laser diode and suggestions on how to focus it.

I'm attempting to build an IR laser pointer.
It needs to operate at 850nm (IR spectrum).
It has to be as close to a "dot" at 250 feet as possible (columnated beam, and not a wide "flashlight" type beam).
Power output should be around 150mW.
I need to control the brightness from 5mw to 150mw electronically. (was considering a driver that could current limit the output variably, or PWM).
The laser module has to be CSEL (Cavity Surface Emitting Laser).

My questions are:

1) any suggestions in finding a CSEL module that would work for something like this, that is reasonably priced?

2) what is needed to select a lens to columnated the beam, so it doesn't diverge like a flashlight?

3) would PWM or current limiting work on a module like this to control brightness?

Any thoughts would be GREATLY appreciated!

Thanks in advance everyone!

 

[berkeman]

Others will give you better thoughts than I can on this, but I had a couple questions to clarify things a bit.

Can you use optics near the far end to focus the laser beam? If the laser beam diameter were something like 10cm there, could you use a lens to generate your focused spot? Also, what is the stability of the air like between your laser diode and the place 250' away? Are you assured that they will be no thermal gradients or other sources of distortion on the beam over that distance?

 

[Mike Gaffer]

Others will give you better thoughts than I can on this, but I had a couple questions to clarify things a bit.

Can you use optics near the far end to focus the laser beam? If the laser beam diameter were something like 10cm there, could you use a lens to generate your focused spot? Also, what is the stability of the air like between your laser diode and the place 250' away? Are you assured that they will be no thermal gradients or other sources of distortion on the beam over that distance?

10cm at 250 feet is acceptable.
Optics / lenses would have to go as close to the diode as possible.
This is for mounting on a weapon as a pointing device - so air stability is not a factor as there will be many environmental influencers.

 

[berkeman]

It would seem that 10cm would be fairly normal for the diameter of a laser (pointer) beam at that distance without any special optics, no?

https://www.physics.utoronto.ca/~jharlow/teaching/lasers.html

 

[Mike Gaffer]

Its my first time using a VCSEL laser -- so I was uncertain if it needed focusing or was just normally columnated to some degree coming out of the module. I own a few of similar hand held lasers to this:
https://www.ebay.com/itm/325596205550
and if I unscrew the lens, the diode module in the back of the receiver/head sink throws a beam that appears to spread at around (estimated) 30 degrees.

 

[Mike Gaffer]

CSEL (Cavity Surface Emitting Laser) - I MEANT VCSEL
Vertical Cavity Surface Emitting Laser...

 

[berkeman]

My Google-foo is not having a lot of luck, but it seems that existing IR laser guided bomb optics would be a good field to look into. Have you had any luck finding references for that field?

https://en.wikipedia.org/wiki/Laser-guided_bomb