10 Mile Distance Laser

[rusirius]

The customer rep for wickedlasers just sent me this youtube video

https://www.youtube.com/watch?v=V8Gex8S6Rjw

They covered 7 miles in the city with heavy light and air pollution using a 2w 445nm WITHOUT a beam expander! The lakes I had in mind are going to be much darker and emptier than this, and i still intend on getting the expander

Remember one thing. This is getting directly in the beam. If the guy shooting the video had put up a piece of cardboard and looked for a "spot" it wouldn't have been there. You can look into the sky and see the moon clearly and brightly, but that doesn't mean you can hold up a piece of paper with your back to it and see it.

What you asked for sounds like you need to be able to measure at what level the dot is hitting once it reaches the other side. On the other hand, if you just need to be able to verify that you can "see" the origin of the beam, then you would be fine.

 

[wellexcel]

Remember one thing. This is getting directly in the beam. If the guy shooting the video had put up a piece of cardboard and looked for a "spot" it wouldn't have been there. You can look into the sky and see the moon clearly and brightly, but that doesn't mean you can hold up a piece of paper with your back to it and see it.

What you asked for sounds like you need to be able to measure at what level the dot is hitting once it reaches the other side. On the other hand, if you just need to be able to verify that you can "see" the origin of the beam, then you would be fine.

Ok, we're going to try it at different distances but we'll see if you're correct about the 7.5 mile span.

If you hold up a piece of paper toward the moon, it's light will illuminate the paper. It just won't reflect like a mirror

I can put a layer of reflective material over the cardboard, or we can just catch the beam with a camera like in the video

And yes, origin of the beam is more important but both would be great

 

[Atomicrox]

I'm tired of arguing this, but as I have said many times I wouldn't go with a 445nm. Low brightness per mW, high scattering, high divergence, dangerous if you mess up.
I'm still convinced low divergence is better than more power (and that it will, in fact, cross 10 miles under good weather).

Keep in mind the "dot" from that WickedLasers video is probably over 10m in diameter (which is why he could stare into it safely - it won't project a well defined dot on cardboard. If all you want to do is "look into the beam" and see the "origin" you don't need anything fancy like a BE or low divergence. Pretty much any high brightness laser will do, so just grab an ebay 532nm pen (for $5) or a 1W 445nm from china (for $80). In fact a 1W 445nm is visible from the international space station (just the "origin", like that video).

 

[wellexcel]

I'm tired of arguing this, but as I have said many times I wouldn't go with a 445nm. Low brightness per mW, high scattering, high divergence, dangerous if you mess up.
I'm still convinced low divergence is better than more power (and that it will, in fact, cross 10 miles under good weather).

Keep in mind the "dot" from that WickedLasers video is probably over 10m in diameter (which is why he could stare into it safely - it won't project a well defined dot on cardboard. If all you want to do is "look into the beam" and see the "origin" you don't need anything fancy like a BE or low divergence. Pretty much any high brightness laser will do, so just grab an ebay 532nm pen (for $5) or a 1W 445nm from china (for $80). In fact a 1W 445nm is visible from the international space station (just the "origin", like that video).

200mW 532nm

https://www.youtube.com/watch?v=F6LSr8-zQDY

If I can save $500 and just pick up any cheap 532nm then so be it, but I want this to work

I feel like im running into circles so I'll give my decision another day to think about

https://www.youtube.com/watch?v=iI7Qq1mYQlI

 

[Alaskan]

445nm is terrible for this test, don't do it!

 

[wellexcel]

Ok, I wont do the 445nm

532nm Green Laser Pointer Light Pen Lazer Beam High Power 5mW 16340 Charger | eBay

Something like this is probably good enough

 

[Alaskan]

That might put out 50-75 milliwatts, 25 percent of that infrared. I have several similar to it, they do put out a nice beam which can go for miles, but not so sure how suitable it will be for your project or stable, they tend to be unstable.

 

[wellexcel]

I just bought it, and since it was so cheap I can still afford something else too in case anybody has anymore suggestions.


Thanks to everyone for their advice

 

[olympus mons]

Question- I imagine that the laser being near perfectly level to the water is pretty damn important. Any tiny degree of angle will be amplified massivly as the beam travels miles and miles. So even if the OP can ensure the host is level will that guarantee the module inside it is also as level? The OP will probably will need a better level than a carpenters level I would guess.
What if the module is a few microns or even 1/2 a mm off in the host? What about lenses. Could the beam not hitting dead center affect the trajectory? I know my 400mW 532 threading is not perfectly tight and throws the beam off quite a bit as I focus it. I can wobble the focusing knob and the beam moves across the sky my many meters.
None of this is a big deal for a handheld hobby laser but the OP is talking about pretty precise measurements. I'm not sure a Chinese mass produced laser is going to be the best choice.

OP- have you looked into surveying laser equipment? You might even be able to hire out a person to handle that end of the project. Those must be pretty precise. I'm not sure what the range is but I am guessing the manufacturer needs to ensure the laser is level in there or it would throw off their results of the survey.
Seems like you need this laser to be pretty freaking spot on level. This isn't as much as a pointer or handheld laser needed but a precisely tuned instrument.

I'm tired of arguing this, but as I have said many times I wouldn't go with a 445nm. Low brightness per mW, high scattering, high divergence, dangerous if you mess up.
I'm still convinced low divergence is better than more power (and that it will, in fact, cross 10 miles under good weather)..

I must say I agree with this. I know I'm new and still learning a lot here but even I can tell you its not very easy to see the spot of a 445 or 450 at a distance. Plus add the terrible divergence I'm not sure why anyone would recommend the OP use a multimode 445 at all. Seems like a terrible choice for many reasons IMO.

 

[wellexcel]

I sent a couple of emails out to some companies but they haven't responded

I don't mind so much anymore, having the perfect device for this would really only be useful for measuring an accurate height difference. That would be great, but measuring the cutoff point is good enough for now

It should look something like this

http://oi60.tinypic.com/210hpwn.jpg
http://oi59.tinypic.com/29omlwp.jpg
http://oi59.tinypic.com/nd06d1.jpg

Regardless of it being a 26 ft dot, it shouldn't hit the other side unless I'm at a height set above that bulge

Hopefully by using the Chinese 532nm, I can measure what exact height it cuts off at

No more cardboard wall anymore either

 

[Encap]

We are going to find out more about the curvature and horizon in this experiment

If it could reach across at say 10cm above water level, that would be significantly amazing.

10 cm? Yes, it would be significantly amazing that perhaps your lake is a flat spot on the otherwise round earth.

Do you actually expect an $9.85 laser, including shipping, will travel 7.5 miles/12000 meters across your lake at 4 inches above the lake water level?

see: Horizon - Wikipedia, the free encyclopedia

 

[wellexcel]

10 cm? Yes, it would be significantly amazing that perhaps your lake is a flat spot on the otherwise round earth.

Do you actually expect an $9.85 laser, including shipping, will travel 7.5 miles/12000 meters across your lake at 4 inches above the lake water level?

see: Horizon - Wikipedia, the free encyclopedia

Sure, maybe even 3 inches :na:. I can always buy something more expensive later. I'm going with the other members on this one


How to Determine the Distance to the Horizon - For Dummies

Could You See the Curvature of the Earth in this Airport? | WIRED

Keep in mind the "dot" from that WickedLasers video is probably over 10m in diameter (which is why he could stare into it safely - it won't project a well defined dot on cardboard. If all you want to do is "look into the beam" and see the "origin" you don't need anything fancy like a BE or low divergence. Pretty much any high brightness laser will do, so just grab an ebay 532nm pen (for $5) or a 1W 445nm from china (for $80). In fact a 1W 445nm is visible from the international space station (just the "origin", like that video).

 

[Encap]

Sure, maybe even 3 inches :na:. I can always buy something more expensive later. I'm going with the other members on this one


How to Determine the Distance to the Horizon - For Dummies

Could You See the Curvature of the Earth in this Airport? | WIRED

Good luck with that ---at least you will gain some experience .

 

[Alaskan]

I wonder how well a high power laser line might work if someone were on the other end of the path and watching for a peak in level when sweeping up and down? One question I've had for awhile, still unanswered, is how divergence applies to a laser line, anyone know? Is its divergence as far as the line getting thicker the same? Does it diverge the same amount as a spot would? If so, how can I reduce its divergence to keep the line as thin as possible for as far as possible?

I've asked here before, crickets on this one so far!

My apologies for quasi-high jacking the thread with this question, but the answer might be useful for your project too.

 

[Atomicrox]

I just remembered something relevant to this topic. A few years back I used to live in a far less polluted city that had a lot of open areas. I once pointed a 30mW 532nm pen from the top of a tower to a building ~3km away and the dot could be seen without any effort (of course it was many meters in diameter, not good enough to point at cardboard but good enough to see).

Good luck!

 

[wellexcel]

I wonder how well a high power laser line might work if someone were on the other end of the path and watching for a peak in level when sweeping up and down? One question I've had for awhile, still unanswered, is how divergence applies to a laser line, anyone know? Is its divergence as far as the line getting thicker the same? Does it diverge the same amount as a spot would? If so, how can I reduce its divergence to keep the line as thin as possible for as far as possible?

I've asked here before, crickets on this one so far!

My apologies for quasi-high jacking the thread with this question, but the answer might be useful for your project too.

No problem at all, ask any questions you have

Good luck with that ---at least you will gain some experience .

Very true, thank you

I just remembered something relevant to this topic. A few years back I used to live in a far less polluted city that had a lot of open areas. I once pointed a 30mW 532nm pen from the top of a tower to a building ~3km away and the dot could be seen without any effort (of course it was many meters in diameter, not good enough to point at cardboard but good enough to see).

Good luck!

:thanks:

That sounds good enough for now, the camera should have a high chance of picking it up (like the videos)


12x30mm Aixiz Laser Mount and Lab Holder | eBay

I just bought one of these for mounting to a tripod, so I almost have everything I need now. Should be able to finish this project before next month ends