Recommendation for long range laser diode?

[k28336548]

I'm looking for a small, visible and harmless laser that would have a minimum range of 600 m and with a divergence less than 300 mm in diameter at 600 m. By range I mean it can still be visible clearly regardless of day or night.

It has to be small in size, perhaps a laser diode, and it'll be fired in pulses.

It's going to be used for combat training game (laser gun) and I want to integrate into my system with micro-controller control.

Is there any recommendation?

 

[Speedy78]

Visible and harmless never really go together. If it's being used in a manner where safety can be assured at all times then you could do it. Also at 600m during the day you will need a lot of power to see it. Tell us a little more about your project.

 

[Antharak]

Wow. 600m. the only thing that can be seen at that range in day light is targeting lasers used by the military. They are IR and in the tens of watt level. Safety can't be assured at that level of power. It's good that you are concerned about safety, but it just can't be done.

 

[Shakenawake]

I am consitently impressed with the incredible divergence of the LPC 826 diode. It's dot stays very small at incredible distances. it's red dot is only visible at extreme range in low light or dark conditions, though I am willing to bet that in the day time if someone went and stood by the target, they could see the dot, maybe with a high enough powered scope you could see the dot.

as the others said, safe and very visible is not really possible. even a 555nm 5mW laser dot would not be visible 600m away in the day time I am willing to bet

 

[DrSid]

It's not as much about diode, as about optics. You need single mode laser, that's for sure. But rest of the problem is on optics side. Generally speaking, to improve divergence of a laser, you need to increase it's output aperture size - in other words the beam must be thicker when exiting laser.

0.3m diameter at 600m means 0.5 mRad divergence. That does not sound that unreal.

to get 0.5 mRad you need this formula:

divergence = (2 * wavelength) / (aperture_diameter * pi)

from that you will get

aperture_diameter = (2 * wavelength) / (divergence * pi)

using wavelength 650nm (red, which is cheap), and divergence 0.5 mRad you'll get required output aperture of 0.8276 mm.

That is quite usual aperture size for modules we use for building lasers, or for hobbyist lasers sold everywhere.
Now aperture size is not only thing limiting divergence, there are other, like spherical aberration of the optics system. But it should be main factor and it should give you rough idea.
But as guys already said .. it won't be safe. Safe is 5mW. 5mW laser spread over spot 300mm in diameter will be visible in total darkness .. but that's it. Never in daylight, much less in full sun. In full sun even that 250mW might not be well visible at this spot size.

You could also use green lasers, which will have better visibility (roughly twice), but will be more expansive.

Maybe you could try one of these, and see how it's going ..

http://www.o-like.com/index.php?mai...oducts_id=18&zenid=3n6rib33i9f4m406v0pl0jhot3

http://www.o-like.com/index.php?mai...ducts_id=340&zenid=3n6rib33i9f4m406v0pl0jhot3

 

[k28336548]

Thanks so much for all your info. Sorry I've forgotten to mention that the laser should be emitted in pulses and only emitted when the trigger on the gun is pulled so it will only be emitted for a few milliseconds. If take this into account, high power lasers won't be harmlful don't they?

If say price is not really my main concern. I might be looking at those military grade targeting laser. Do those IR lasers go way further than red and green lasers?

Any recommendation on military grade or long range(600m) harmless(in this case) targeting laser diodes?

 

[DrSid]

If it's to be VISIBLE at long range, it will have to be dangerous at short range. It's like you would want to have gun which will shoot 600m but will be harmless. It's not possible.
IR will require a bit wider beam, as it has longer wavelength, but since we are talking 1 millimeter, it should not be a problem. But of course, it wont be visible at all.
If you want the beam to be detectable on that distance, that is different thing entirely.

 

[Shakenawake]

I can see the dot of my lpc 826 from a mile away, I measured today. only in low light or dark though as I said. single modes are all pretty good it is true, but this one in particular still beats the others I own.

and yes, high powered lasers can be dangerous even for durations of under a second

 

[3Pig]

I can see my 200mw 532 (Probably under 120mw of actual green) at about 250-300 meters in broad daylight. but its certainly not eye safe.