Claimed laser pointer range - is it just pure hype???

[luvlasers]

You quite often come across retailers who claim their lasers have a range of x kilometers. Sounds pretty impressive and got me excited. Going through basic divergence calculations though and things don't add up.

Take for instance one retailer (no names, keep this thread clean) who says their laser pointers have a range of 20 miles (32 kilometers for those of you in practical countries ). Fair enough, maybe they do. Just say they have a divergence of 1.0mRad (which is most unlikely) then at 32 Km, what will the beam size be???

1.0mRad means 1mm divergence for every 1 meter - at 32 000 meters you'll get a divergence of 1x 32000/1000 to give a divergence of 32 meters.

So unless i have my numbers wrong (if so, please break it to me gently) at the claimed range of 20 miles, the beam diameter will be 32 meters.

Seems pretty stupid to claim a range of 20 miles when your beam diameter is the size of a major building.

In theory, laser light is just light which has an infinite range so its not completely wrong but comes across as mis leading.

 

[Aseras]

no matter the range it won;t be a beam or a dot anymore even good collimted laser beyond a few hundred yards are flashlights.

fwiw the laser reflectors on the moon are hit with 2.3 watts of laser power.. the "beam" with them is several miles across. hitting a traget about 1 sq foot. of that only about 1/100th of a precent of the original light is returned to earth, and it's still bright enough to detect.

 

[FNinjaP90]

I for one hate the concept of a laser range. I think it's a marketing ploy to wow unsuspecting buyers. In theory, every laser has an infinite range, with the apparent brightness at any range purely dependent on the output power, wavelength, beam divergence, and the amount of particulates in the air.

There is no way you can prove that your laser has a range of 20 miles instead of say, 15 or 25 miles. If your laser's dot is visible 20 miles away, it will also be visible 25 miles away, except dimmer. The number is just made up in my opinion, unless there is a standard mathematical formula to calculate "laser range". Given the wide range of "laser range" between different sellers with lasers of similar power output and divergence, it doesn't look like this standard formula exists.

 

[liveforphysics]

Just for a kinda rough idea of distance possible, I am able to reflect one of my 100mW DX lasers off a skycrane(only aiming at the skycrane to avoid possibility of hitting a humans eyes, even though at those distances divergence should keep it safe) in the Seattle skyline, while standing on the roof of my Microsoft building in Tukwilla (about 12miles away).

Now, it requires a very clear night just to get to see the seattle skyline, but when conditions are right, I'm definately able to see the reflection off the crane.

That means light is traveling 12miles to the target with enough intensity to reflect some tiny tiny fraction of it BACK 12miles to finally reach my eyes.


Now, while night skiiing on a perticularly foggy day, I was barely able to get the beam to reach 200yards (note that it was a different laser, but still very powerful).

None of this is any sort of scientifically measured quanitative data, just personal observations, but it does give you a general idea of what you may expect to see.

 

[Aseras]

seeing the dot reflect back at a range wholly relies on the reflectivity of the surface you hit. the furthest I've seen a laser go is from my engineering building down the intracoastal waterway about 9 miles, I can hit a navigation refltor and see it as a very bright dot.

having somone at the range and having them see the dot is another matter. I'll bet anyone actually looking for a laser ( or really a flash of whatever color, red or green ) as far away as you can put them will see the laser. beyond a few hundred yards as I said, you really no longer see a beam but rather a brilliant flash of light as the "beam" intersects your vision. the closer the brighter. as a distance it looks just like any other flashlight might look, except it comes out of nowhere and goes away just as fast.

 

[stevetexas]

I'm not even sure why they post "range" on the advertisements. How many of really USE a laser at a distance of more than a few meters? Most of us proably use these in our garage or workshops.

For astronomy and pointing, seeing the beam go out is nice, but does it really matter if it goes 5 miles or 50? The importance is that you can align your optical device with it, but even a visible beam that extends 1/2 mile would probably do the trick for amateur astronomers.

 

[comozo]

Distance claims all depend on the yardstick by which a particular retailer defines it based upon the divergence and mw output and wavelength specs.
It can be defined as
1. The distance with which a light color object can be illuminated and the reflected light still visible to the laser user under optimal night time [or daytime] conditions
2. The distance a person having a clear line of sight can see a lasers point of origin.
3 The distance at which a surface can be seen to be illuminated with an observer standing next to the surface.
4 The distance with optical aids; applies to 1 and 2
So your right unless there is a standard or the retailer specifies what they mean it is hype.
I for one only use a laser at distance, I couldn't care less about burning stuff, shining it in my bedroom or anywhere in the house for that matter. That only leaves using it outdoors. Range for me is important as defined by number 1. Every once in awhile I'll but new lenses and decrease the beams divergence for the heck of it.

 

[allthatwhichis]

This brings a question to my mind... Is there a way to make a laser with "perfect" divergence? Or is that an oxymoron?

 

[pseudonomen137]

This brings a question to my mind... Is there a way to make a laser with "perfect" divergence? Or is that an oxymoron?

Unfortunately no. You can get divergence extremely low, but technically never at 0. Mathematically speaking, if you collimated a laser with a "perfect" lens at a beam diameter of infinity grin2: ), that would be the only way to get 0mRad divergence.