Laser throw questions, calculations, looking for some very throwy laser (10+ Km)

[Barkuti]

This is a question I am making for a good friend of mine, he's not into the forums thing and doesn't speaks english so, well, let's say from now on I speak in his behalf.

First of all I will say he is already experienced with laser use, I know he had a green Prome 303 he got from somewhere which a few months ago broke, and I got another unit for him at laserpointerstore. He also told me that for a brief time he had a far more powerful device a guy sold him second-hand, with more than 10x the throw (!) of an 80 mW green Prome 303 which he rates at ≈1 Km, which he also broke down while using it likely of overheating. I have no details of such thing worth mentioning other than he said it was from a military

source, or that is what the other guy told him.

Since I am a DIY guy and like flashlights (you can also find me at BLF - http://budgetlightforum_com/ with the same nickname) he thought I could build (!) or find some commercially available laser which could meet the above requirements. But seriously, I've read some bits here and there and I'm not sure. In the thread Help to get 8km throw distance ( https://laserpointerforums_com/threads/help-to-get-8km-throw-distance.75152/ ) here, joeyss said “Without a beam expander a laser with 1.4 mRad would have a beam size of 11 meters at 8 km away”, but how is this calculated?

I've been taking a look at the laserpointerstore ( https://laserpointerstore_com/ ), they sell a 3x Magnification Optical Expander ( https://laserpointerstore_com/collections/laser-accessories/products/3x-magnification-optical-expander ) which is listed as being compatible with the Thor and Gatling series. Given the specifications the Gatling Stretch ( https://laserpointerstore_com/collections/green-lasers/products/gatling-stretch-laser-pointer?variant=32104056258605 ) looks to be the farthest throwing thing, with a 1000 mW green, 2.4 mRad, and listing “<8 mm at 10 meters beam diameter”. If that is correct, the beam diameter would be <8 meters at 10 Km, which would shrink down to <2⅔ meters with the aforementioned beam expander, or <3 meters at 11.25 Km. Did I cook all of this right?

Well, this is all for now. Looks like I sort of cooked an answer here, but of course I'd like to see some worth witnessing expert opinions, including some other product suggestions if you will. Thanks for everything.

P.S.: I need to reach 20 posts to post links? Seriously? How is that of help? Makes me waste more time, and is less convenient for you too.

 

[Snecho]

Welcome to LPF. The 20 posts link thing is because of spammers that make a new account and try to advertise and post links to "miracle keto" and stupid a$$ sht every single night.

I know it's really unfair to new members who are legitimately looking for help.

 

[Cyparagon]

“Without a beam expander a laser with 1.4 mRad would have a beam size of 11 meters at 8 km away”, but how is this calculated?

Trigonometry. mRad is short for milliradians. Small-angle approximation applies here and is as follows, X mRad divergence will be [X*(distance in meters)] mm at (distance). For instance:
1.4*8000=11.2 meters.

As far as "throw distance", last I remember, you flashaholic types actually have an objective formula for that. Distance where lux drops to some number, yes?

You can convert laser power to lumens by using the luminosity function. I googled this, but there are ones with more granularity. 80mW of green for instance is about 47 lumens. Since lux is a lumen per meter squared, the rest is basic geometric algebra.

2.4 mRad, and listing “<8 mm at 10 meters beam diameter”.

That's contradictory chinese copy-pasta nonsense. Online laser retailers regularly lie about specifications.

 

[Barkuti]

… The 20 posts link thing is because of spammers that make a new account and try to advertise and post links to "miracle keto" and stupid a$$ sht every single night.
…

Wellp, that is some sort of common problem in forums. From time to time some new user appears and posts something with some dubious link(s), seen that in BLF more than once. They may be starving but that is no license to be bad, imho.

Trigonometry. mRad is short for milliradians. Small-angle approximation applies here and is as follows, X mRad divergence will be [X*(distance in meters)] mm at (distance). For instance:
1.4*8000=11.2 meters.
…

Mmm, yes last night I read something related in the corresponding Wikipedia article ( https://en.wikipedia_org/wiki/Milliradian ), but then I was lured with the nonsense specifications of the above given laser.
So we don't really know what the actual divergence of the aforementioned lasers is, or not unless someone tests them. Any sort of technical tests available?
I also find suspicious to see 1.2, 2.4 and 3.6 mRad typical values given for red, green and blue lasers. Smells nonsensical. I wonder what the actual numbers are, probably a lot closer than the given figures?
To make some calculations, given that 2.4 mRad green laser (?), at 10 Km its uncorrected aperture is 24 meters, while its corrected one is 24 m / cos (0.0024 rad) = 24.000069120166 meters. Now I see why it is approximated.

…
As far as "throw distance", last I remember, you flashaholic types actually have an objective formula for that. Distance where lux drops to some number, yes?

You can convert laser power to lumens by using the luminosity function. I googled this ( http://hyperphysics_phy-astr.gsu.edu/hbase/vision/efficacy.html ), but there are ones with more granularity. 80mW of green for instance is about 47 lumens. Since lux is a lumen per meter squared, the rest is basic geometric algebra.
…

Yep the ANSI-NEMA FL-1 bla bla bla ( https://flashlightwiki_com/Light_Output_Measurements ). So throw = √(luminous_intensity/target_illuminance), being target illuminance defined as 0.25 lux for the FL-1 standard, throw in meters and candelas for luminous_intensity. But if you use a flashlight in well lit areas like a city's outskirts at night, or close to wherever public lighting is, the useful throw is less due to the ambient light.
I take note with the lumen conversion thing, even if it is biased. Not all humans see the same, but probably this probably is topic for another thread. And glad to see laser power is measured “out the front” or effective radiant power.

So, gd one step further. As I see this now, and presuming the actual divergente of lasers is tighter than those advertisement figures, a very powerful blue one could also be worth it.
What is a beam expander? Probably some small aspheric or plano convex lens enclosed into something? But then “beam shrinker” would be a more correct name, as I want to make it converge. As far as I see it “expanding” a beam is diverging it. This smells like the usual thing of using “warm white” to speak about low correlated temperature led emitters, and “cool white” for high CCT ones. But of course, I'd like to hear what you have to say.
Basically, if we are to get a powerful, quality laser, it's a good start. Plus then, some sort of “beam expander”. I wonder, in the same way as aspheric collimator flashlights work, if we could make some sort of support assembly with a laser beaming through a focused aspheric lens, and attain a multi-kilometer throw with ease. Well, sounds pretty feasible.

Soo, any good recommendations for a good start laser wise? I guess it's not only power, but also whether if its stock lens is good or not…

 

[hwang21]

You are gonna want excellent beam quality for those km throw goals -> TEM00 would be best (gaussian intensity profile), which means you will need a DPSS laser. 532nm green would probably be your best choice, if more expensive than direct diode lasers. This will get you started in the right direction: https://www.jetlasers.org/index.php?id_product=10&controller=product

A beam expander trades beam diameter for beam divergence - by increasing the beam diameter, you decrease the divergence by a proportional amount (I forget the exact math now, perhaps Cyparagon can chime in)

 

[Alaskan]

That's the last place I'd ever buy a laser pointer, that is a rip-off highly overpriced web site for lasers. Aside from trying to ward people off from buying from them, here's my contribution:

Laser Divergence Calculator - divergence matters: Beam behavior over distance

The beam divergence describes the widening of the beam over the distance. It is defined in milli-radiant (mrad), which usually describes a part of the circumcircle. Generally spoken, it is best to have a divergence as small as possible. The beam...

www.laserworld.com

Just for fun: At closest, the moon is 225,000 miles away, at furthest about 252,000 miles. When at 225,000 miles a 1 mRad 4mm wide beam leaving a laser pointer theoretically produces a spot which would be about 9.5% its diameter, at apogee 8.5%.

 

[Snecho]

That's the last place I'd ever buy a laser pointer, that is a rip-off highly overpriced web site for lasers. Aside from trying to ward people off from buying from them, here's my contribution:...

That's a very harsh thing to say about JetLasers

 

[steve001]

This is a question I am making for a good friend of mine, he's not into the forums thing and doesn't speaks english so, well, let's say from now on I speak in his behalf.

First of all I will say he is already experienced with laser use, I know he had a green Prome 303 he got from somewhere which a few months ago broke, and I got another unit for him at laserpointerstore. He also told me that for a brief time he had a far more powerful device a guy sold him second-hand, with more than 10x the throw (!) of an 80 mW green Prome 303 which he rates at ≈1 Km, which he also broke down while using it likely of overheating. I have no details of such thing worth mentioning other than he said it was from a military

source, or that is what the other guy told him.

Since I am a DIY guy and like flashlights (you can also find me at BLF - http://budgetlightforum_com/ with the same nickname) he thought I could build (!) or find some commercially available laser which could meet the above requirements. But seriously, I've read some bits here and there and I'm not sure. In the thread Help to get 8km throw distance ( https://laserpointerforums_com/threads/help-to-get-8km-throw-distance.75152/ ) here, joeyss said “Without a beam expander a laser with 1.4 mRad would have a beam size of 11 meters at 8 km away”, but how is this calculated?

I've been taking a look at the laserpointerstore ( https://laserpointerstore_com/ ), they sell a 3x Magnification Optical Expander ( https://laserpointerstore_com/collections/laser-accessories/products/3x-magnification-optical-expander ) which is listed as being compatible with the Thor and Gatling series. Given the specifications the Gatling Stretch ( https://laserpointerstore_com/collections/green-lasers/products/gatling-stretch-laser-pointer?variant=32104056258605 ) looks to be the farthest throwing thing, with a 1000 mW green, 2.4 mRad, and listing “<8 mm at 10 meters beam diameter”. If that is correct, the beam diameter would be <8 meters at 10 Km, which would shrink down to <2⅔ meters with the aforementioned beam expander, or <3 meters at 11.25 Km. Did I cook all of this right?

Well, this is all for now. Looks like I sort of cooked an answer here, but of course I'd like to see some worth witnessing expert opinions, including some other product suggestions if you will. Thanks for everything.

P.S.: I need to reach 20 posts to post links? Seriously? How is that of help? Makes me waste more time, and is less convenient for you too.

What you have not considered is the angular resolution of human sight. Another thing to consider is the reflectivity of a surface. Best results are white ones. Specular reflection I don't consider because it is a specular reflection. However, that will increase the distance considerably. I've experimented with a 122 mw 532 laser with a divergence of less than 1mrad I was just barely able to see a spot on a light colored building at almost 15000 feet. A +500 mw 532 laser it was more visible. As for specular reflection I was able to see a bright reflection off a window at about 31380 feet with 5 mw of 532 nm light. 3 miles out, 3 miles back. Report back when you have results. Attaching a laser to a spotting scope or telescope and looking through the eyepiece gives better results.

 

[Barkuti]

Just dropped by to say thanks everyone, among a few other things.
First one is, had a brief chat conversation with my friend and, when I said around ≈€300 as a first shoot … I just don't think he wants to spend the serious money this deserves or needs.

Jokes aside, took a look at some of the available videos in the Jetlasers store. In Simple Comparison of 532nm, 445nm, 405nm, 473nm, 635nm PL-E Pro series JETLASERS ( htt ps://www.youtube.com/watch?v=2iKUcJ1KmKs ) there are some huge differences in the out the front beam width of these pointers, but after taking a look at this ( htt ps://www.laserworld.com/en/laserworld-toolbox/divergence-calculator.html#divergence ) laser divergence calculator, I understood that is no big deal.
So basically, besides output power a low divergence and a powerful beam expander is all what seems to matter. Jetlasers has a 10x beam expander, something I didn't find at Laser Pointer Store or Sanwu lasers, by the way.
Different to the usual flashlight stuff where emitter intensity and optics size and shape is usually what matters most, nonetheless.

 

[steve001]

Just dropped by to say thanks everyone, among a few other things.
First one is, had a brief chat conversation with my friend and, when I said around ≈€300 as a first shoot … I just don't think he wants to spend the serious money this deserves or needs.

So basically, besides output power a low divergence and a powerful beam expander is all what seems to matter. Jetlasers has a 10x beam expander, something I didn't find at Laser Pointer Store or Sanwu lasers, by the way.
Different to the usual flashlight stuff where emitter intensity and optics size and shape is usually what matters most, nonetheless.

Not so fast. A beam expander helps alot, but there are limits as I mentioned earlier. No matter how low the divergence might be a laser beam in the far field expands in a linear way just like a flashlight beam does. There will be a limit to seeing a spot at distance. By the way, what is your throw distance goal?

 

[Cyparagon]

...24 meters, while its corrected one is 24 m / cos (0.0024 rad) = 24.000069120166 meters. Now I see why it is approximated.

Yeah, I wasn't saying "small-angle approximation" in a general sense. I mean there's an actual, specific usage with that title used commonly in the maths:

Small-angle approximation - Wikipedia

en.wikipedia.org

As for the intensity... heh. quarter lux isn't very useful, especially if you're viewing something under quarter lux from hundreds of meters away or whatever. But at least it's objective. I never cared for that "SOO BRIGHT" review nonsense

In any case, I could use the practice so I'll go through an example:
1. Quarter lux is quarter lumen per square meter.
2. Green light is ~590 lm/W. Re-arranged, this is 1lm=1/590*watt
3. We want to know at what distance the power density is quarter lumen per square meter
4. substituting, we obtain .25/590W per square meter.
5. Assuming a circular "top-hat" beam profile with 0mm initial beam diameter and 2mRad divergence for simplicity, and
6. referring back to X mRad divergence will be [X*(distance in meters)] mm at (distance)
7. power density = power/ beam area = 80mW/(pi*(2*distanceInMeters)mm/2)². Simplified:
8. power density = 80/(pi*distanceInMeters)² mw/mm². Setting power density to expectation:
9. .25/590 W/m² = 80/(pi*distanceInMeters)² mw/mm². Convert units, then cancel units:
10. 4.24*10^-7 = 80/(pi*distanceInMeters)²
11. distanceInMeters = √(80/(4.24*10^-7))/pi
12. distanceInMeters = 4370

That's what 5 minutes of my rusty math shows anyway. Feel free to correct if I fuxored something. 4.37km "throw" sounds pretty reasonable for a mid-power pointer. All else equal, a 1W green with 2mRad would be "15km" throw, which is about the biggest we build around here. Beam expanders of course will put this number WAY higher, to the point where atmospheric disturbances render this basic geometry stuff useless.

 

[lazeristasUVISIR]

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What is a purpose to shoot that far?