Laser beam visibility and power.

[Laser Chick]

"I am not sure if being nearly 50 times brighter will mean being able to see it from 50 times further away."
Good question but no as it is not linear. I believe it is a 4 to 1 ratio if I remember correctly.

 

[Tre]

Ok I have the 1 watt 520nm diode set up in a massive heat sink with a plug in power supply. Twice in different locations I set the laser pointing straight up and walked away until I could not see it any more. Both times I got about a half mile (measured by google maps) though at that point it was so dim that I had to look straight at where it was and pan my eyes up and down to catch a glimpse. With light pollution it really is not drawing attention past a few hundred meters and is impossible to see over a half mile. I am wondering how much more visible it would be in the middle of nowhere.

When I get back home next week I will post a new thread showing the very simple build.

 

[Atomicrox]

I can only see my 3W 450nm from a few tens of meters away when pointed up, but then again I live in a big city with a lot of light everywhere.

 

[Alaskan]

But, when I point my 1 watt expanded 520nm green or blue (@4 W) at a high cloud base, I can clearly see a bright spot, so I guess this means someone viewing the spot from a mile or more away will likely only see the spot moving around on the cloud? How cool - That might get some people scratching their heads.

 

[Davidx]

Really interesting thread. Wondered the same thing many times.

Tre, keep up your experiments and keep us updated. + Rep for you

 

[joeyss]

But, when I point my 1 watt expanded 520nm green or blue (@4 W) at a high cloud base, I can clearly see a bright spot, so I guess this means someone viewing the spot from a mile or more away will likely only see the spot moving around on the cloud? How cool - That might get some people scratching their heads.

did this with 400mw of 532 back in high school and a telescope that had 50 times expansion It was snowing. I only had 10x binoculars ,but i looked through it and saw a big dot.Thing came out like a green spotlight in lighting up all the snow. Also used that telescope when I was in 11th grade to test what I termed laser induced fluorescent lighting with my 405 ( this was before bmw came out with them.) I'd get the fluorescent dot to go 100 feet in my yard at night only using my 50mw 405



Also I saw a vid a few years ago from a news station on here of "footage of a ufo"? Everyone on here knew it was a 445. It was the beam going up to the clouds.

 

[Pi R Squared]

Also I saw a vid a few years ago from a news station on here of "footage of a ufo"? Everyone on here knew it was a 445. It was the beam going up to the clouds.

:crackup::crackup::crackup: I bet that has happened many times, even in the middle of the night you know there is going to be someone else outside somewhere that can see that spot on the clouds, if they aren't laser hobbyists like us they are going to think UFO.:crackup:

Alan

 

[joeyss]

:crackup::crackup::crackup: I bet that has happened many times, even in the middle of the night you know there is going to be someone else outside somewhere that can see that spot on the clouds, if they aren't laser hobbyists like us they are going to think UFO.:crackup:

Alan

i wonder what my 3 watt 445 would do... But I don't want a fake ufo sighting...there's a reason for that guys and its NOT attracting attention it's something else.let's say i was in the right place twice at the right time with my DSLR and 20x80 binos

 

[Encap]

Ok I have the 1 watt 520nm diode set up in a massive heat sink with a plug in power supply. Twice in different locations I set the laser pointing straight up and walked away until I could not see it any more. Both times I got about a half mile (measured by google maps) though at that point it was so dim that I had to look straight at where it was and pan my eyes up and down to catch a glimpse. With light pollution it really is not drawing attention past a few hundred meters and is impossible to see over a half mile. I am wondering how much more visible it would be in the middle of nowhere.

It depends on the many factors of air in "nowhere". :can:

At sea-level, one cubic inch (1 inch x 1 inch x 1 inch) (16.39 cm3) of "air" contains approximately 400 billion billion (4*1020) air molecules, each moving at about 1600 km/hr (1000 miles/hr), and colliding with other molecules and anything else they come into contact with about 5 billion times per second. This is the reason for "air pressure". The amount of particles in that air that can reflect a portion of a laser beam's light back to your eye determines if you can see it or not.

It all depends upon atmospheric conditions--a beam you can see extremely well in fog or area with high concentration of particulate matter in the air can be almost invisible in clean clear air

Laser beam visibility is highly dependent on ever changing atmospheric conditions and aerosols in the air.
You never actually see the laser beam --what you see is the reflections from particles in the air.

"In a vacuum, the laser beam itself would be invisible - regardless of power or color. As a laser beam passes through Earth's Atmosphere some of the photons encounter large airborne particles which reflect some of the light back to an observer. This only creates intermittent tiny bright flashes of light or "knots" in the beam - it is not why we can see the beam itself.

It is extremely small airborne particles called aerosols having a diameter significantly less than the wavelength of the light that causes the beam to become visible.

The effect of minute particles scattering light is called Rayleigh scattering and it's most noticeable effect is to turn the daytime sky blue. Rayleigh scattering causes photons to be scattered in a roughly spherical manner around these particles. Some of the light is scattered forward (in the direction of the beam), a lesser amount is scattered to the sides and about the same amount that is scattered forward is scattered backwards towards the light source. This backwards scattering is why the beam is more visible to people standing near the astronomer using it, than people standing some distance to the side. The more of these minute particles there are in the atmosphere, the more Rayleigh scattering there is."
From : RASC Calgary Centre - The Atmosphere, Astronomy and Green Lasers

Really you need to understand aerosols in air --is very interesting actually--you need to know what they are locally and density of same to be able to figure laser beam visibility possibilities of one place compared to another place on the earths surface. Example: the most aerosol-laden air in the United States today pales in comparison to Asia. So laser beams are more visible there, generally speaking. Depending on the season and weather conditions, surges of aerosols can make their way into the atmosphere almost anywhere on Earth

See NASA Earth Observatory page for an excellent explaination of aerosols in air with lots of pictures and charts of the planetary distribution of aerosols : Aerosols: Tiny Particles, Big Impact : Feature Articles

PS Merry Christmas

 

[Tre]

How's that for a simple build?

 

[diachi]

Is that just a solid chunk of aluminum for a heatsink? No chance of that getting too warm!

 

[Pi R Squared]

i wonder what my 3 watt 445 would do... But I don't want a fake ufo sighting...there's a reason for that guys and its NOT attracting attention it's something else.let's say i was in the right place twice at the right time with my DSLR and 20x80 binos

If you are saying what I think you are, I too was in the right place at the right time twice in my lifetime. I also wouldn't want to create a false UFO sighting. I hope I get to see something so incredible again a third time before I pass on.

How's that for a simple build?

You should resize your photos before posting them, it's not that much trouble. Surely you don't really want to make the thread completely useless to tablet users and to some of the phone users.

Alan