Curving green laser lights

[tbak]

Hi everyone,

Last time I was at Burning Man at night I noticed a strange phenomena. Someone from 1 or 2 km away was shooting a very bright green laser into the sky at a shallow angle. Instead of the light going in a straight line into the sky, it seemed to bend downwards and disappear over the horizon. There were mountains in the horizon and the light would appear to fall behind them.

Attached is a photo explaining what it looked like. The thick green line is the apparent path of the laser.

Has anyone seen this before? Do you know what would cause the laser to curve downwards like this? I have asked around but nobody seems to know.

Regards,

Tom

 

[Grix]

Most likely an optical illusion.

 

[DrSid]

Temperature gradient could easily bend it .. I've just haven't ever really seen it.

 

[comradmax]

Same thing that creates mirages, the atmosphere bends the light and you can see object that are beyond your horizon. The air is not uniform, there is a big change in temperature and density with altitude, also local atmospheric conditions will have an effect. The result is that the air acts as a giant lens. Also related to the reason why sky is blue and sun is red when it's low.

 

[DrSid]

How is the bending related to blue sky ?

 

[IsaacT]

I experience this bending pretty much every time I go outside at night to shine my green laser. When the angle approaches the horizon, the atmosphere appears to bend the path more and more. Think about if you were inside a glass sphere. You point your laser up at a 90 degree angle and not much would change(I don't think, never been trapped inside a glass sphere though), but if you instead shined it at an angle close to a tangent, the glass would take the laser light and throw it in an arc. I think we all see that from time to time when our lasers hit a curved surface. Since the earth IS a sphere, and the atmosphere acts like a lens, it makes perfect sense for the light to react in such a way.

This is just the way it made sense to me. If there is a flaw in my understanding please point it out so we can all be educated.

Peace,
Isaac

 

[JLSE]

Temperature can play a big role.

To see what heat can do, try this..

Turn any laser on and aim it across the room, the further the better.
Take a small butane torch and use it as if you are trying to 'heat'
the bottom of the beam.

You will notice that the beam will move horizontal, left to right.

Now take the torch and act as if you are 'heating' the side of the
beam. You will now notice that the beam moves vertical up and down!

You can repeat quite an accurate 'control' over the beam simply by applying
heat from a flame. Apply the flame close to the source...

I can only imagine what the heat from the ground does when it rises and
passes through it, and over great distance...

The example ive mentioned works well as close as 5-10ft. The further
the dot is away from the source, the easier it is to see.

Try it :beer:

 

[comradmax]

The light goes is straight lines in glass. There is one point of bending where it enters, air and glass have a different refractive index. When light encounters the glass for the first time it will bend at a specific angle. It will go through the glass straight until it hits the end of glass and the start of air, it will bend at an angle here again. If the glass edges are parallel, the light will come out in the same direction as it entered, but shifted over to the side. If you make the edges at an angle, you created a prism or a lens.

If the material somehow varies its refractive index, then you can get a curved path of light. Air's index will change with temperature, so like Dr. Sid said, it will create a gradient. What you have here is a slightly bent medium (from the curvature of Earth) with a varying refractive index. The light will follow some path continuously bending.

 

[Aussienitro]

How is the bending related to blue sky ?

It isn't, well not really in the sense that one would think. Blue sky is the result of the atmosphere scattering the lower wavelengths of light so it looks to be coming in at all angles not just from the sun, thus at dusk its red as the light has to penetrate further and the blue light has been diffused. Look up rayleigh scattering for a better explanation.

 

[DrSid]

It isn't, well not really in the sense that one would think. Blue sky is the result of the atmosphere scattering the lower wavelengths of light so it looks to be coming in at all angles not just from the sun, thus at dusk its red as the light has to penetrate further and the blue light has been defused. Look up rayleigh scattering for a better explanation.

Well I think there is no relation. But comradmax seems to think otherwise.

 

[Aussienitro]

Well I think there is no relation. But comradmax seems to think otherwise.

Interesting to note that water is the opposite, red light is absorbed more thus deep sea plants are often red to make use of the green light that does make it there. Green chlorophil would reflect it.

 

[DrSid]

Btw. I could not find it anywhere .. but IMHO warmer air (less dense) will have faster speed of light then colder air (more dense) right ?
In such case, with warm air just above the sand and cooler air above, the beam should turn up, not down.

 

[JLSE]

Btw. I could not find it anywhere .. but IMHO warmer air (less dense) will have faster speed of light then colder air (more dense) right ?
In such case, with warm air just above the sand and cooler air above, the beam should turn up, not down.

If you read my post above, a simple experiment will
demonstrate exactly what you are asking.

From what can been seen, heat changes the angle
but I dont think it can bend. That is unless over great distance
with similar patterns of rising heat repeating itself. This
would result in 'section' of differing angles. I wouldn't say bent.

Rising heat seems to affect the beam by shifting it horizontal.
To shift it vertical, heat must be applied from the 'side'.


*EDIT*

The only other thing I was thinking is the heat from the
ground is more radiant in nature, but this if im not mistaken
would cause aberrations and just make it 'look' larger by
'vibrating' the beam. Unlike using a torch which is
more controllable and focused.

Or am I off on that??

 

[comradmax]

Well I think there is no relation. But comradmax seems to think otherwise.

I apologize, I was actually wrong about that. Sky and sun color are due to Rayleigh scattering, like was mentioned.

 

[nikokapo]

schlieren effect wiki - Google Search

Can't really add more to what the guys have said already

 

[BKarim]

the ground was very hot in this desert and the night air much cooler.
so there was a high gradient in the density of air , like the gradient of density in optical fibers