Laser beam visibility and power.

[Tre]

Ok, a 30mw laser beam perpendicular to line of sight is only visible from about 10 meters away. This is because most of the light is either reflected straight back off of particles or slightly redirected away from the beam.
What I want to know is how much power one would need to make a laser "beacon" that is visible pointed straight up from over a mile away on a clear night.

 

[Pi R Squared]

Ok, a 30mw laser beam perpendicular to line of sight is only visible from about 10 meters away. This is because most of the light is either reflected straight back off of particles or slightly redirected away from the beam.
What I want to know is how much power one would need to make a laser "beacon" that is visible pointed straight up from over a mile away on a clear night.

Unless it's green 532nm or 520nm you're going to probably need several watts, I don't know the answer but I have seen video of a green laser that was taken from several miles away and it was easily visible even when pointed straight up, am sure it was probably a few hundred mW. There are many low powered lasers that can put a dot on the clouds or something miles away but the beam itself won't be visible from the side. You must go with green. Hopefully others will comment on this.

Alan

 

[chaos1267]

I'd like to test this when I get the chance unless someone beats me to it or finds related material. Depends on when a (trustworthy) friend and I are both off at night. I just got an olike 450mw green and a 800mw ple pro so I'd love to give this a try. Probably will be a couple days until then though.

 

[Laser Chick]

What Pi said!
Friends in the mountains out west tried different WL hand held lasers and the conclusion was go with 532nm as 405nm, 445nm and 650nm did not create a beam that was very visible from several miles away.
445nm at 4W+ was a runner up.

 

[VisibleGreen]

Yes this is nothing that hasn't been done already as the hobby has been around for quite a long long time. Before you do these tests though it would be wise to learn about proper safety and handling. These can cause permanent eye damage.

 

[RedCowboy]

Humidity levels will impact this, just think about how bright lasers look on a foggy night.

 

[Alaskan]

It sure helps to have fog, or rain, if not too heavy. I am also very interested to know how far away a 1 watt output 520 or 532nm laser beam can be seen in the distance. I've seen some YouTube videos of someone sweeping the horizon trying to spot on their buddy with a camera and man, was I less than impressed with how much the beam will diverge at the end of the beam to turn into no more than a spot light five miles away, but what a spot light it is! If you do this experiment, I'd love to see the comparison between a 1 watt green laser with and without a beam expander on it.

 

[GSS]

I'd like to test this when I get the chance unless someone beats me to it or finds related material. Depends on when a (trustworthy) friend and I are both off at night. I just got an olike 450mw green and a 800mw ple pro so I'd love to give this a try. Probably will be a couple days until then though.

Its an awesome morning for lasing here in MA, overcast light drizzle im located in the highest part in the city and perfect for doing this test but no "trustworthy friend" just people who see the news and would love to complain. I cant seem to get anyone interested in this hobby, just my brother in law but he is just to busy and one friend that is somewhat but he lives in CA. Not to start a political issue im just venting as not all days are perfect like this and wish someone close might come around:cryyy:

 

[RedCowboy]

You can see the top of Stone Mountain from the high rise hotels in Atlanta, I have been in plenty of them.

I have been tempted to rent a balcony room facing east and do some testing late night when no one else will be on top of the mountain except me or my helper. I have climbed up it on the 4th of July and watched firework explode towards our faces, yes I got up there and found about 100 other like minded knuckleheads, it was incredible, and loud, sorry I didn't get any video, it was years ago, probably wouldn't be allowed to do it now.

Distance is in the 12 mile range.

 

[Tre]

I was not expecting this topic to get such good responses, ok here is some more backstory.

We (my uncle, his friend, and their families) were packing up from a trip to the desert and I was shining around my 30mw greenie, my uncle asked how long it would run and suggested that we could leave it upright to be able to locate the camp while driving the razor at night. I told them that the beam was not very visible from far away and demonstrated it by having one of them hold it pointing straight up and the other one walk about 30 feet away. I told them that it is possible to get up to one watt lasers and I would look into it.

So I was thinking a 1 watt 520nm from dtr's with the preset driver and lenses, strap it to the cpu heatsink that I have with resistors feeding the fan, all of it hooked up to the solar charged battery bank that he has on his trailer. The Idea is to use it far in the desert.

 

[Pi R Squared]

Don't you think others would see it? Try using a GPS instead. Don't attract attention to your location like that, it's not a good idea, even in the desert.

Alan

 

[Tre]

Don't you think others would see it? Try using a GPS instead. Don't attract attention to your location like that, it's not a good idea, even in the desert.

Alan

Yes, we know that and it is not a concern as the places we camp dont have much aircraft but do see a lot of trailer campers with buggies, light up flagpoles, bonfires and other attention draws.
I just found out that my uncle bought a diode already so the beacon build is rolling forward.

 

[Trendkilla254]

Yes, we know that and it is not a concern as the places we camp dont have much aircraft but do see a lot of trailer campers with buggies, light up flagpoles, bonfires and other attention draws.
I just found out that my uncle bought a diode already so the beacon build is rolling forward.

I will require the host to be in the following format:

 

[Pi R Squared]

Yes, we know that and it is not a concern as the places we camp dont have much aircraft but do see a lot of trailer campers with buggies, light up flagpoles, bonfires and other attention draws.
I just found out that my uncle bought a diode already so the beacon build is rolling forward.

Be sure to keep us updated on this and let us know how well it works, try to make sure someone can't come and steal it while you're gone. Also let us know if black helicopters land at your campsite.

Alan

 

[RB astro]

try to make sure someone can't come and steal it while you're gone.

Alan

Yeah, and imagine if someone does find it, and doesn't realise the danger of the beam and sustains eye damage.
Liability?
Hmmm, I don't think I'd even consider doing something like this.

 

[Tre]

D:
It would be on top of a trailer and only be on when there would be people in camp and awake, moved inside when we went to sleep. Thanks for the warnings I will keep them in mind. The good thing is that the ladder on the trailer is high enough that children who could not understand and obey the warnings would not be able to climb up anyways.

We recently went out again and I put my 30mw green laser pointing towards some sand dunes about a half mile away. When we drove up and turned off the light we could see the beam overhead over a foot wide. Another time I set the laser pointing straight up and I was able to faintly see it from over 50 meters away.
I am not sure if being nearly 50 times brighter will mean being able to see it from 50 times further away.