A Unique Use for Lasers

[Meatball]

At 300mws, 650nm does alright as a 6 ft spot if its viewed from a distance. But the red is insignificant if you are view the spot up close. If you use the laser just past the end of the yellowed western sky, the spot should be useable for pointing at large distances.

Focus is entirely up to you.

The 6ft spot will be painful to look into- for brightness' sake. I would have to condemn the action of looking back into the beam - at any distance or spot size. Keep this laser dot off of humans, or anything you would not shoot for that matter.

 

[Picksmither]

Hogs are considered red-green color blind and have been shown not to have L cones. However, as Dogs Best Friend said, the green cones extend up to at least 650nm, but probably a little higher. Assuming humans are considered not to be able to see above 750nm, but we can actually see a little further into the infrared than that (some individuals much more than that). I'm hoping to take advantage of this dimmer view of red that hogs have compared to humans. If I focus the light just wide enough to see them at 100yds I'm assuming they will see a very dim dot pointing at them. (like looking at a near IR LED, cherry red glow). I'm assuming this will not be enough to spook them, but that's just an assumption.

On the other hand: digital camera CCD's, according to this graph, show peak sensitivity between 600-800nm. So if I use either 650nm or 780nm it could show up better on CCD without an IR filter than with the naked eye. BUT...I really don't want to deal with mounting a digi cam to the end of the scope and having to worry about eye relief and overglow giving away your position.

The ND3 was kind of my inspiration for this project. I found out from a spec sheet that the ND3 uses a combination of a 5mW and a permanently spotlighted 18mW greenie. I hear that you can really see it, but so can the hogs.

@Meatball : Thanks for the real world testing! That's what I was looking for. I think that viewing it through a good scope will help gather a little more light than the naked eye. Sounds like a 200mW may work, but may still be bright if looking back at it, but I don't intend to point it at anything I am not willing to shoot, so eye safety is not a big factor.
I'm sure I've got something wrong here, but wouldn't that much power spread over 6ft instead of 1mm mean that it would actually not appear all that bright?

 

[Dogs Best Friend]

I'm sure I've got something wrong here, but wouldn't that much power spread over 6ft instead of 1mm mean that it would actually not appear all that bright?

No, you are right.
a 200-300mW laser would be pretty dim when it is unfocused to a 72 inch diameter. If you do the math (I used a 2mm beam):

72"/2 = 36" = r
(Pi)r^2 = (3.14)(36in^2) = 4069in^2


compared to:

2mm = .08"/2 = /.04" = r
(Pi)r^2 = (3.14)(.004in^2) = .005in^2




.005/4069 = .0000012

So, the energy per square inch of an unfocused laser beam at 72" diameter is almost one million times weaker than that of the same beam focused to 2mm.


Lasers burn because they concentrate a small amount of energy, so un-concentrated laser light cant really damage anything. An unfocused beam would definitely not hurt anything. That being said, it's still not a good idea to point a 200mW laser at anything you do not intend to shoot; you cannot always judge what the beam diameter will be at any given distance.

I would still be very interested to know if pigs can see 660nm light...

 

[Picksmither]

@Dogs Best Friend I really appreciate you doing the math on that one. That's what I figured, but I am new to all this. In theory this setup would be eye safe as long as you don't focus it down too much or the eye is not too close to the focal point. Does the inverse square law still apply with lasers?

Would the recoil be a problem with a high quality build? If so, how could I compensate for this?

I'll be using a shotgun shooting slugs and the recoil is pretty heavy.

 

[AUS]

OK i did a very quick and dirty practical test..

This is a Mitsubishi 638nm diode driven to about a "guestimated" 1 watt (its one of the Mitsubishi 500mW rated ones).

Admittedly the optics on this are just O-like glass lenses and you would do better with higher quality glass.

I focused it to a circle just under a metre diameter (about 2-3 feet) at about 20 metres (say 60 feet). The lamp shade is about a metre in front of the wall i was focusing on. I zoomed in the camera to take the photo. While you can clearly make out the lamp, it gets fairly dim much bigger than this or much further away than this. And much more power and you will need cooling to leave it on for long periods of time.

It should be possible to build something dedicated for the task with several high power diodes in an array, but I'm still not sure how you would go further than this.

 

[nouthyella]

If you are looking just for illumination, you should consider using a phlatlight RED which is crazy bright and will help to flood a wider area.. but i think it might scare them at close range..

A phlatlight, being an LED, will have a significant amount of light below 650nm, which will scare the pigs.

 

[Picksmither]

@AUS thanks for the quick and dirty test. Honestly, that amount of light is more than enough for my purposes. All I need is to identify where to shoot and that can be done with a vague silhouette. But I have favor to ask. I noticed in your signature that you have several 300mW 660nm lasers, could you try the same test with one of these? 1Watt is a lot, and 638 is supposed to be much more visible.

 

[AUS]

I noticed in your signature that you have several 300mW 660nm lasers, could you try the same test with one of these? 1Watt is a lot, and 638 is supposed to be much more visible.

I have a few 660nm laser diodes in the 200mW-300mW range but none mounted in a host and working at the moment. If I get some time tonight I'll see what I can do.

I'd like to try a longer range shot outside but laser pointers over 1mW are illegal here so I have to be careful wandering around with one.

I also have a red LED torch I'd like to try (i suspect its about 640nm) which is fairly monochromatic although has a hint of yellow and green when looked at through a diffraction grating.

I really think an infra-red scope and 1watt 850nm laser diode would be better and easier to use, although I believe some states have laws against this in the US? There is a youtube video of someone shooting pigs using IR gear (in Hawaii I think).

 

[EliteGeek91]

To Pick, my dad and me use green lasers, and lights while hunting hogs. I thought hogs can't see green. So it's worse than red? Cuz we shine ND5's at them, and they never look up.

I also would be very interested in making my own "ND5", for alot less.

 

[Picksmither]

@elitegeek91 Hogs can actually see green just as well as we humans can. It could be argued that they are a little more sensitive to blue than green though. They can't differentiate green and red because they can't see the color red, but they can see red light. They just are not as sensitive to it.

Hogs in general do not respond to being shined with a spotlight of any color as long as the brightness is not too high. Vision is their most important sense, smell is. If their sense of smell is not alerting them to trouble (ie you are upwind) then they aren't likely to trust their vision. But they are incredibly intelligent and learn quickly that they get shot at after the lights come on and then they start to spook easy. That's why I am trying to build a laser light that they either cannot see or can barely see, but we can see just fine. Thus the possibly magic 650-660nm window.

From what I understand any focusable green laser of sufficient strength would work great as a stand-in ND5. They use 18mW lasers, but they are safe because they cannot be focused to a point, they are always spotlights (the way I understand it). Also, if you buy a laser over 5mW it may leak heavily into the infrared and could be dangerous.

 

[Picksmither]

@AUS stay safe and don't get in legal trouble, totally understand if you can't get caught outside with one. Anyone else could maybe try a 650nm 200nm at long range?

If I were to build a 1W IR laser, what is the cheapest place to get the diode? They are still pretty expensive aren't they? Expensive meaning >$75 total build.

Also the digital camera without an IR lens will be more sensitive to 600-800nm than we are. In theory, I may be able to use a digital camera instead of the naked eye with a 660nm and still be able to see it???

Also, anyone know about gun recoil and lasers?

 

[AUS]

You can get 1W IR 808nm diodes from ebay for $15 or so, 850's are dearer though. I have an 850 build into my might vision gear which i can barely see as dark-cheery red glow. It just got dark here i might have a play soon.

There are plenty of laser sights for firearms including automatic weapons, so i wouldn't worry about recoil too much if the thing is well made.

 

[AUS]

OK i did another test with a (I THINK) 660nm laser. This is a bog standard 5mm red closed can diode from a generic DVD burner, again at about 60 feet. I ran this one at 90mA and it was starting to get warm. A VERY rough guess I'd say it was probably 100mW or so.

By the way, I took the 638nm 1 watter outside briefly and shone it into the golf course behind my house with a wide beam (it would have looked more like a dim spotlight than a laser). I think it would definitely be possible to hunt with it if you knew roughly where to look first. I didn't hang around long enough to take photos though.


NOTE it looks brighter in the picture than it did to my eyes. I saw it as more red but the camera shows it as a pinky colour.

This was in a power supply, I'll see if i can mount this in a host and get a longer outdoor shot with it. Underneath this is the original 1 watt 638 pic.

And the 638 1 watt:

 

[Picksmither]

Wait, what?! How does a 1W 638 show up significantly less bright than a 660 100mW??? You said the color was more pink and it showed up a little brighter in the picture, but is it true that the 660nm was more bright in person?

If that is true, then I am going to go ahead and order a 200mW 650nm from lazerer like this one:
LZCS - 650nm 200mW Focusable Red Laser Pointer

Then if it doesn't turn out to be bright enough for my needs then I will have the housing and battery to swap out a 1W IR diode and driver. But if digital cameras without the IR filter can pick up 650nm better than the naked eye, I may just leave it red and mount a camera anyway before converting to IR.

Thoughts everyone?

 

[AUS]

No, the 638nm looked brighter to my eyes than the 660nm.

The camera seems to pick up 660nm better than 638nm and also make it look pinker than it appeared in real life. I suspect the camera's CCD is more sensitive to the longer wavelength than my eyes are.

When i compared them side by side the 660nm looked more red and the 638 looked a lighter red, not quite orange but getting there.

 

[Picksmither]

Ok, thanks AUS. That's what I figured was happening. I still think I will stick with the 650nm even though it is not as visible to the naked eye. I will probably mount a camera on it anyway to get a better view. Later building the laser into a full on Infrared. AUS I really appreciate you doing some real world testing for me. We'll see how it goes, but I am hopeful for this project! Going to go order now!

Anyone have any input before I order?