The BEST green laser for keeping its intensity over distance?

[VioletLasers]

My house is situated out the country, about 5 miles away in one direction is a hill, so one day we decided to test out the lasers. We literally took turns driving over to the hill to shine back the lasers and compare brightness at that distance. Believe it or not the laser that came out on top happened to be a 200mw green fixed focus pen.

I haven't bought lasers in a a wile, so now i'm doing some online shopping again and here's the thing, i want a green laser that will beat our 200mw pen from such a distance, so i am looking at a 500mw green laser on o-like Powerful Crown upgrade 500mW green laser torch/waterproof [OL-532-500] - $274.99 : Zen Cart!, The Art of E-commerce this price for such a beast is reasonable in comparison to other sites however, that's not what i'm concerned about! Will a focusable green laser ever be a powerful at distance as a fixed, since even the slightest turn left or right of the focus head will widen the beam significantly at a distance right?

My only option is to maybe find a fixed green laser with a separate focusable head or a focusable one that can be switched to infinity and locked into place.

Thanks to readers any suggestions on lasers?

 

[lasersbee]

Any Laser that goes through the Earth's atmosphere will
decrease in power over distance. Even more so if there
is more suspended particulate in the air (humidity...
dust... rain... pollution... etc).

It is an obvious conclusion that increasing the number of
photons (Higher mW output) will increase the distance a
Laser beam will travel through the same air..


Jerry

 

[crazyhobo]

You should look into beam expanders.

I have a $20 7X monocular that works wonders.

I've put a tiny spot on water towers miles away. It's awesome.

 

[numquamretro]

what expander ist that you use? since i am building up a new handheld with 800mw+ i wonder if i can integrate a beam expander in the housing. shouldnt two lenses work as well?

 

[crazyhobo]

This: Amazon.com: Brunton Echo 7x18 Pocket Scope: Sports & Outdoors

I removed the prisms to improve transmission. This required moving the small lens outside of the housing though since removing the prisms increased the focal length. For high power you might need to get a beam expander made for lasers. I shone my 445 through this assembly once and the refections started melting the inside of the monocular.

 

[numquamretro]

This: Amazon.com: Brunton Echo 7x18 Pocket Scope: Sports & Outdoors

I removed the prisms to improve transmission. This required moving the small lens outside of the housing though since removing the prisms increased the focal length. For high power you might need to get a beam expander made for lasers. I shone my 445 through this assembly once and the refections started melting the inside of the monocular.

you are probatly right, this thing maight not hold up with the heat. Thats why i thought about doing it with lenses only. And on the other hand i am very limited with the space in my handheld housing.

 

[crazyhobo]

Will a focusable green laser ever be a powerful at distance as a fixed, since even the slightest turn left or right of the focus head will widen the beam significantly at a distance right?

You should be able to obtain the same size dot with either one with a little effort.

Assuming your green 200 mw pen has a divergence of 1.2 to 1.5 mRad, if you shone it through a 7x beam expander the dot 5 miles away would be 1.4 to 1.7 meters!