# Need laser capable of 2500 ft with focused fine point of light

#### RogueRose

Joined Oct 10, 2014
375
I want to do an experiment where I need a laser capable of projecting a fine point of light at ~2500 ft. I'm not sure how much laser beams expand as they reach out further, if this is negligible or if it is enough that I need to look for a specific type, lens, etc. I need the light to be able to shine on a target (like a tape measure, grid, etc) that is denominated in at most 1/4", probably down to 1/16" - though the beam/dot can be larger than 1/16"^2 or even 1/8"^2, the finer, the better.

I need to measure very fine adjustments in the laser's level and be able to see on the target/grid where the light falls and how the adjustments effect the beams destination.

I have virtually no practical experience with lasers outside of playing with pointers. I need to know what power and wave length to look for. If a red or green is adequate. I assume the green ones will reach that far as we have been told airline pilots had problems with them (though I'm suspect of these claims - especially when they say they caught the individual doing it - I mean really? how they do that!?).

#### oz93666

Joined Sep 7, 2010
722
Commonly available lasers have very divergent beams ...Even at 25 feet they would not give the results you require .

You are asking too much , what you want is not possible without spending $100,000's and the laser being 10's meters long ... Even with a good laser , the turbulence in the atmosphere would prevent it . Pilots are drama queens , exaggerating , they would be able to see a laser accurately aimed at them , but it would be dim ... The military have been trying to use lasers to blind enemy pilots in combat , they need MASSIVE lasers , even then , not easy. Thread Starter #### RogueRose Joined Oct 10, 2014 375 Commonly available lasers have very divergent beams ...Even at 25 feet they would not give the results you require . You are asking too much , what you want is not possible without spending$100,000's and the laser being 10's meters long ...

Pilots are drama queens , exaggerating , they would be able to see a laser accurately aimed at them , but it would be dim ...

The military have been trying to use lasers to blind enemy pilots in combat , they need MASSIVE lasers , even then , not easy.

Thanks. That is disappointing. I had a really interesting experiment lined up if this was possible. I still may be able to make it work with a standard laser but it won't give the accuracy I was hoping for. Luckily I can use a powerful scope in place of a laser with similar results but the laser would have made it more visually "acceptable".

As for the pilots, I always wondered about that, I has strong suspicions that what was being reported was BS. I saw reports on the national news about this and thought it was impossible, especially the part where they said they arrested the person for assault with the laser. I always wondered how they could find the person on the ground, let alone pinpoint exactly where it came from even at say 7500 ft let alone 30,000+. The reporters must think the public will believe anything.

#### ericgibbs

Joined Jan 29, 2010
9,300

#### oz93666

Joined Sep 7, 2010
722
hi RR,
Airline pilots being temporarily blinded by idiots, who use green lasers to flash onto low flying aircraft cockpits is not BS
I have a number of lasers ,,, Even with the very best quality available the beam diverges from 1mm to about 5mm within 10 meters

This means at 2Km the laser dot would become 1 meter in diameter ... that's 1 W power spread out to 1 meter diameter
And that's before interference from the atmosphere ... the pilot would see a faint light ...
A search confirms this , saying this only a feasible danger during take off and landings ,'distracting' pilots when the laser could be within a 100 meters or so of the aircraft...

There are reports (June 2018) , of Chinese "fishing" boats firing lasers at US military aircraft ... to date with no success , no blind pilots , and we can imagine these boats will have big lasers , 10's of meters long , allowing for a tighter beam.

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#### ericgibbs

Joined Jan 29, 2010
9,300
hi oz,
My commercial laser ranger used Triple Gallium Arsenide 904nm emitters for ranging upto 5000 mtrs, using a cooperative target ie: 10cm Dia Prism.
The 30pps beam, 30nSec On period from the diode was focussed using a lens, set to give a beam diameter 0.8mtr at 1000mtrs.
The deliberate beam spread is essential so that the ranger operator can aim and track a moving target.
Used for Land and Marine surveying.
E

#### oz93666

Joined Sep 7, 2010
722
hi oz,
give a beam diameter 0.8mtr at 1000mtrs.
The deliberate beam spread is essential
That sounds about right eric ... but you're implying this spread is deliberate , and if required you could choose to have a small dot at 1000meters ... this is not my understanding ...

Important to clarify we are talking about laser diodes ... these have revolutionized lasers and are in all the pointers and levelers , very rarely above 1W in power , they look like this , about 10mm round ...

And often come in a housing with a small adjustable lens ... But due to the small size , it's my experience , no matter how you adjust the lens , the divergence is still there ...

There are bigger lasers , other types , and this greater length allows for a tighter beam , and more power . It must be these the Chinese are using without much success ... and of course the US military has a converted 747 with a laser the whole length of the craft for shooting down missiles in flight , but it has to be above 90% of the atmosphere , otherwise scattering would prevent it working.

#### shortbus

Joined Sep 30, 2009
7,326
The reporters must think the public will believe anything.
You don't get Fox news channel where you live?

#### dl324

Joined Mar 30, 2015
9,546
You don't get Fox news channel where you live?
Hopefully some future FCC will require them to take the "news" out of their name. They've had so much propaganda that I now distrust anything from FOX; even though some of it is legitimate. When the local news people started spouting propaganda, I lost faith in the veracity of anything from FOX.

#### MisterBill2

Joined Jan 23, 2018
4,820
My suggestion is to visit the laser seller that I have used in the past. The site was "LASER66", the company is "creative technologies".
A bare laser is about as useful as an LED, you need one with a driver circuit and a lens.
For far better laser packages, but at a lot more money, check Edmond Optics. They have a good selection of laser devices, but they cost a lot more. But their catalog will give you a good idea as to what is available.

#### shortbus

Joined Sep 30, 2009
7,326
Hopefully some future FCC will require them to take the "news" out of their name. They've had so much propaganda that I now distrust anything from FOX; even though some of it is legitimate. When the local news people started spouting propaganda, I lost faith in the veracity of anything from FOX.
Saw last evening the pres wants to start a new channel, USA International or something. It would be government funded to combat the "fake"/bad press he gets. Real story.

#### dl324

Joined Mar 30, 2015
9,546
It would be government funded to combat the "fake"/bad press he gets.
State run media, like other authoritarian regimes? If that happened, it would probably be time to move to Canada.

#### ebeowulf17

Joined Aug 12, 2014
3,024
EDIT: I've deleted my political post. Off topic. Sorry.

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#### MisterBill2

Joined Jan 23, 2018
4,820
I am suggesting that we return this thread to the original questioning. Political ranting belongs elsewhere, OK!!!

RR was asking about a laser with a small spot at half a mile. The cheap, \$19 boresighted ones we used had a spot about 2 inches in diameter at around 200 feet. so you will need to spend a bit more a bit more than that.