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Keeping a small dot over one mile distance

srow

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I am very new to lasers. I need to be able to fire a laser over a distance of one mile and keep the dot small enough and bright enough to be seen at the other end. I have purchased three lasers two of which didn't have the enough power(1mW) and one 2W(LuckLaser cost £80) which didn't keep a small dot over the distance. The dot became so large after over 100m that it couldn't be seen. Before I buy another laser disaster is there anyone that can help please?
 



VisibleGreen

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I am very new to lasers. I need to be able to fire a laser over a distance of one mile and keep the dot small enough and bright enough to be seen at the other end. I have purchased three lasers two of which didn't have the enough power(1mW) and one 2W(LuckLaser cost £80) which didn't keep a small dot over the distance. The dot became so large after over 100m that it couldn't be seen. Before I buy another laser disaster is there anyone that can help please?
Inherently light will lose focus over large distances. It's just how it works. Light spreads out even for a laser.
Those cheapy lasers won't have great specs unfortunately.
More power isn't the answer either because increasing the power just makes it brighter, not smaller or larger and those higher power diodes as suggested don't produce a dot but rather a line. It's the cost of having a multimode diode.

What you want to do will require a lab style laser with certain optics. That's quite a feat to keep the dot the same size after a mile. You're best option is a single mode diode like the 16x 405 diode here

It's the most powerful single mode we have in a diode for now.

Although you would do well with either this or this

Please guys if I'm wrong feel free to correct me.
 
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Gabe

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VG, while the 16X has wondrous divergence, it would be near impossible to see the dot from so far away due to how 405nm plays tricks with our eyes and makes the dot look fuzzy after a long distance. Although, I'm not sure if this affects everybody. I'm also not sure how long a mile seems to an observer. I mean, I know it's 1,760 yards and 1.609 km, but I don't have enough life experience to tell, so I wouldn't know if 100mW of green will be visible from that far.
 

VisibleGreen

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VG, while the 16X has wondrous divergence, it would be near impossible to see the dot from so far away due to how 405nm plays tricks with our eyes and makes the dot look fuzzy after a long distance. Although, I'm not sure if this affects everybody. I'm also not sure how long a mile seems to an observer. I mean, I know it's 1,760 yards and 1.609 km, but I don't have enough life experience to tell, so I wouldn't know if 100mW of green will be visible from that far.
Well I assumed he was using this for hunting since he wanted to see at long distances. I mean who can see a dot at one mile away anyway? lol
Maybe an eagle?
 

Gabe

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Well I assumed he was using this for hunting since he wanted to see at long distances. I mean who can see a dot at one mile away anyway? lol
Maybe an eagle?
Ah, I suppose. However, on nights when it's raining I can project the spot of my 300mW green onto tr bases of clouds, that has to be at least 2km, no? Although I'm not sure if OP wants tone able to see the dot during the day.
 

Laser Chick

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Is this going to be used to align something like microwave dishes on a tower/post or an antenna where there is somebody looking for the dot at the other end?
Or are you pointing it at something and need to see the dot a mile away as in pointing something out at an open strip mine or long distance surveying?
1- Where are you from/where does it need to ship to, the UK?
2 - What is your budget?
3 - Is this being used in the light of day or the dark of night?
For what you need it is not going to be cheap.
For visibility and a tight beam you should get 532nm and to tighten up the beam at a mile you will most likely need a beam expander also.
You are probably looking at around $700 to $1200 total.
A lot more than £80 but what your application calls for is an elephant gun(1 mile) not a toy BB gun(50 feet).
Just letting you know that I have what you need.
 

VisibleGreen

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Ah, I suppose. However, on nights when it's raining I can project the spot of my 300mW green onto tr bases of clouds, that has to be at least 2km, no? Although I'm not sure if OP wants tone able to see the dot during the day.
Well when it rains the clouds drop in height greatly and the actual size of that dot has got to be massive ;)
This one is just going to be impossible sad to say :cryyy:
 

srow

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Thanks for all your responses. I'm in the UK. It's a flat earth experiment I'm trying to conduct on a lake. The curvature of the earth gives a 50mm hump in the middle so I want to set the laser at 15mm above the water at one end to see if this hump actually exists. If it doesn't exist I would expect to see a the laser at 15mm or lower on the other side. I think the best time for me to conduct the experiment is in the evening at twilight. I'm not sure of my budget, maybe 150 to 300 dollars.

I would like to be able to fire it over 2 miles if possible because the hump would be 200mm instead of just 50mm.

I've been recommend a 3 element lens but I really have no idea what that is or does.
 

Gabe

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Thanks for all your responses. I'm in the UK. It's a flat earth experiment I'm trying to conduct on a lake. The curvature of the earth gives a 50mm hump in the middle so I want to set the laser at 15mm above the water at one end to see if this hump actually exists. If it doesn't exist I would expect to see a the laser at 15mm or lower on the other side. I think the best time for me to conduct the experiment is in the evening at twilight. I'm not sure of my budget, maybe 150 to 300 dollars.

I would like to be able to fire it over 2 miles if possible because the hump would be 200mm instead of just 50mm.

I've been recommend a 3 element lens but I really have no idea what that is or does.
A 3 element lens allows for better divergence at the cost of more power loss. Divergence is how much the beam spreads out, better divergence means less spreading. Will there be a person at the other end looking at the dot?
 

olympus mons

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There was another person on here about 9 months ago trying to do the same exact experiment. You should try to find his thread there was a lot of good information in it. From my memory the thoughts were this.
Even if you could afford a laser powerful enough for the other person across the lake to see the dot at a mile away, the dot would be 10-20 feet accross even with a beam expander on a 532nm laser. You would need many W of 532 power in a lab laser and a huge ass wall for it to reflect off of. So unless you have a 5 figure budget I wouldn't waste anymore money on cheap hand helds. Possibly surveying instruments would do it but that would be your best bet.
 
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Shakenawake

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Get a laser using the lpc 826 diode and a 3 element lens. I believe sci-fi lasers sells them or try blord, a member here. Its a very cheap setup with amazing divergence, I can see the dot of mine a mile away in dark conditions, though probably not 2 miles. Its a red laser. And yes I measured the distance
 

Teej

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Or just save your money..... the earth is round.... :crackup:
:crackup::crackup::crackup::crackup::crackup:



Just a little divergence would "prove its flat" though.

:D

Seriously, a rifle scope and target boat is all you'd need.

Aim the waterline mounted scope at the stern's water line bullseye, fix it in place, and move the boat progressively further away. As it gets further away, the waterline bullseye will dip below the horizon in the scope's field.
 
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