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FrozenGate by Avery

Focus at 1000-3000ft? What is needed?

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fastline

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Dec 21, 2011
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We are still working on a security IR beam and need to focus a beam on an IR collector for switching. Actual power is not yet known but relatively low power if we can focus the beam reasonably at long distance.

I am curious if an adjustable collimating lens will allow focus of the waist at long distance or if that waist typically occurs much closer with available optics, forcing us to work within a very low divergence beam?

For these distances and our needs, we would need about a .2mrad beam which does not seem very common. Not even sure if a typical collimating lens can do it. The plan was to purchase an Aixiz module and use a standard IR LED but not sure what all will be needed yet.

Again, the actual power required will be only the median power required to operate our photo switching devices which should not take too much if we can focus appropriately.
 





You would need a beam expander plus a good focusable IR laser. The beam expander will probably cost more than the laser!
 
The optics side of this has proven quite a challenge because not many people sell reasonable optics for this stuff and if so, not enough information is provided to use them. Will acrylic lenses work for this or will it be quite an advantage to use glass?
 
It probably wouldn't be too hard to jig something up with just a couple lenses, do some google searches of "beam expander" and you'll find two types: Keplerian and Gallilean. I prefer the Gallilean type. Easy enough to make if you can get cheap lenses of the apropriate curvatures and some kind of fixture to hold them in place.

Buying a beam expander will set you back anywhere from <$100 to >$400.

As far as lens material, it depends on how much power you're starting with, and how much needs to get to the target. AR coated glass lenses have much less loss than plain acryllic.
 
fastline said:
The plan was to purchase an Aixiz module and use a standard IR LED but not sure what all will be needed yet.
Click to expand...
Do you mean IR laser or are you looking to use IR LED?

Will this be an indoor or outdoor installation & which country will it be used in?
If indoors will there much sunlight from windows?
 
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To make a beam interruption detection at such ranges, do no rely on the light reaching the sensor alone.

You should use encoded modulation for the transmitter to begin with, and transmit the signal at a predetermined singal rate. IR remote controls for televisions etc rely on the same principle to make them very immune to interfering sources at the wavelengths used.

The advantage of using a carrier wave is that your signal does not need to be stronger that the background, just more specific. In case of a security application you would need to use some predetermined signal to avoid the option of tampering with the system, although that is not an issue with simply transmitting a legible signal over great distances.
 
USA private use, outdoor installation. We own an engineering firm and machine shop so really only limited by lenses and better understanding of the subject. Not really educated on optics much.

maybe some ignorance on LEDs but as I understand, the term "laser" is just an LED with an integrated collimating lens mounted to it? I had the thought is using a narrow FOV LED, mounted into an Aixiz module or similar that can provide focus.

I am not familiar with beam expanders other than they seem to be standard practice in telescopic and microscope optics.

I agree on the emitter/receiver signals but that is mostly a non-issue at this point. We have programming experience with a variety of PICs. The real stumper for us right now is that damn laser and the optics.
 
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A beam expander does two things... As the name suggests, it expands the beam of the laser and 2, it decreases the divergence of the lasers output. If you are using a relatively strong laser, you can use a beam expander in order to hit targets far away, with enough density to transmit a signal.
 
Lasers aren't just focused LEDs. LEDs & lasers both use a semiconductor light source but thats about it.
 
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Lasers are definitely not just focused LEDs.

Here is a picture of a typical 5.6mm laser diode:
D6505I.jpg


You best bet would probably be 780nm CD laser. Even though you may be able to see it slightly (at low power you would only see it as a dim red dot when close to it at night), they have much better beam specs than many other ir lasers. You should be able to focus one at distance pretty good.

If you need it to be totally invisible then you can get a laser diode at 980nm.

780 and 980 diodes are easy to find on eBay. You can find them already in modules with drivers for less than ten dollars.
 
My apology. My understanding was most of these small, low power lasers were actually glorified, focused LEDs.

I have noticed a few beam expander lenses on egay. Not make specs on them which I think makes them worthless but curious if there are any USA resources that don't charge arm/leg for lenses that actually have specs on them?
 
I'm afraid it really isn't likely that your going to be permitted to uses IR lasers for a security device in the USA. Even visible lasers probably won't work out.
Because lasers are highly focused they pose an eye hazard. Since IR is invisible or at least very dim it poses a much more severe hazard. Even low-powered visible beams must remain at least 2.5 meters above ground. Its not going to provide much security when people can walk right under it.
In the USA laser products are regulated by the CDRH (Center for Devices and Radiological Health).

If you try to ignore the CDRH you will leave yourself & your company open to lawsuits in addition to legal consequences.

This is the reason you don't see security laser beams available other then in movies. There are some short range barrier beams but they either are focused LEDs or carefully designed to be below the maximum permissible exposure levels.

There are plenty of other security solutions.
 
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Thanks! it seems most of the ones on egay do not have many specs other than power and wavelength. Would I be taking one of these apart to add an expander lens

The dim light may not be an issue, especially as a first revision. Obviously you would have to be looking for it to see it anyway but my concern is moisture conditions outside that might illuminate the beam well. That may prove a time when this device will not work anyway though. Certainly needs some testing.
 
Halo, this is a private use item. Though I do understand the concerns and regs regarding the issue, these will be used cautiously on a large rural property. I don't think we will run into too much issue. Seems a long list of people on youtube already building burning lasers and all. We only need enough IR to make our sensor happy. Obviously the less the better.
 
Youtube? Seriously, your using random people on youtube as an example of how its safe or you just aren't likely to "run into too much issue"?
We have these things called 'laws' that require a bit more then just saying you will be cautious & only use dangerous devices in rural areas. Outdoor "Private use" on rural private property has no effect on whats permitted.

Sorry but there has already been a couple other users looking to use IR lasers in ways that will harm people.

OSHA also has regulations which govern the use of lasers in the workplace.
 
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Would it really be a problem at <5mw?

I don't see how a <5mw laser at like knee or waist level would be dangerous.
 
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