New here, IR narrow beam laser, how to build it

Being new here, I will mention that our primary business is engineering and CNC machining but more or less looking to buy or build some IR lasers to be used for perimeter security. Probably bounce the beam over 1-3 mirrors before spotting on an IR collector.

I experience with electronics and LEDs but little with IR and especially laser optics. I find that buying ready made lasers for our needs are hard to find or very expensive. The goal is a straight, narrow beam over long distance (1000ft optimally) but of this proved hugely cost prohibitive, I would like to learn what is common and easy.

It looks like crystals are commonly applied right at the front of an IR emmiter to focus a beam but I would think only a distant secondary lens could create a near straight beam. If course, if I can find what I need without making, that would be even easier. Making the housings and such are a non-issue but obviously optics are not our bag. I was looking at maybe using a T1.75 IR LED with a front mounted crystal.

Ideas would be very welcome here.

1000ft is approximately 300 meters. You'd need a very low divergence laser for that. A normal laser module and a good beam expander could do it just fine. A single mode IR diode will probably have a good enough beam quality to have a low divergence. Straight AND narrow by the way isn't possible, the narrowed the beam, the higher the divergence. If you really need a small beam profile and a low divergence you'll need a solid state laser. A 1cm beam would end up being ~3 cm in diameter after 300 meter if you have a good laser.

Crystals are not used for focussing, lenses do that. A crystal is for diode pumped solid state lasers, far more complicated than a simple lens.

LED's won't reach 300 meter far, they're like flashlights, you can't get a nice parallel beam from them. What power and wavelength do you need? I can make all kinds of laser modules, if you want a custom one you can PM me with the specs you need.

You can correct laser's very well using a 532nm beam expander, and then the collimation lens, I've got no divergence from a B&W Tek 473nm at 15ft before, AKA beam diameter was the same at the output end as it was on the wall.

Obviously there will be loss from all the optics used.

No divergence isn't possible. You may had the beam waist between the two measuring points which would give the same size at both points, but the beam won't be without divergence. With a good beam quality of a DPSS measuring the divergence can be difficult because of the distance needed.

Bluefan said:

No divergence isn't possible. You may had the beam waist between the two measuring points which would give the same size at both points, but the beam won't be without divergence. With a good beam quality of a DPSS measuring the divergence can be difficult because of the distance needed.

Click to expand...

Yeh your right, give it a 300ft and it'll be quite big I'd imagine.

Thanks for the replies guys. Bluefan, I think the wavelength and power are still a bit in the air at this point. I am sure we can design a collecting circuit for nearly any wavelength so this is mostly a laser dependent project. I want to stay in the IR length range though so it stays invisible unless that puts considerable cost/complexity in the project. Design goals are inexpensive, relatively simple in design, and determine where the practical limits are. I was really hoping this could be an LED with a single lens design.

We buy a lot from the major electronics distributors but not sure where to get the optics side of this. Ie, lenses and such. We can machine barrels if that is required but I know we bought one some time ago for another project that came in a threaded housing to accept lenses. Then an employee made off with it.....still pissed about that..

808nm will be the ideal wavelength, if you did not already know, higher powers in this wavelength are not too expensive.

High powers are multimode - not good for 1000ft distances. You're limited to <200mW and I'm not even sure 808nm lasers in this range are single mode. You might want to consider 780nm instead.

Keeping in mind here that we will be targeting on an IR collector, I would not think it would take that much power to do 1000ft. I have not run any numbers yet and not sure what the glass will do. Just considering some observations of visible gun sight lasers. I would hope as long as the laser reaches with a reasonable target diam, we can make the collector work.

Where does a guy get glass? Or do they usually sell complete expanders with multiple pieces and you just apply it?