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What increases side view of beam?

freak

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What increases the visibility of a side view of a laser beam? (Without depending on particles in the air) Power? Beam width? Magic?
 





D

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The same ones that increase normal visibility. Side visibility formula must be something like (just my thought)

SV= cos(NV)+k(NV)
 
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Actually what makes the beam itself visible is totally dependent on the particle in the air.
A laser is coherent light that travels in a straight line, so the only way you're going to see any beam from the side (light going perpendicular towards the side) is if the light is reflected off of some particle in the air.

For instance, a 5 mw laser in a fog or really smoky room will show the beam very easily, on the other hand if you were in an electronics clean room with perfectly or nearly perfect clean air that are free or particles, you could turn on a 10 Watt green laser in the dark and no beam would be visible at all; only the spot it produces at it's termination point.
So beam visibility cannot be used as a tool to tell you how much power you have, it's fully dependant on particles floating in the air.
You can however, compare two lasers side by side and the more powerful will be more visible, but without the particles there is nothing. So your laser may have a very bright beam one day and much less the next, it just depends on what's floating around.
 

Grix

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I think there are more photons reflected from the air into your eyes because of the angle, I've tried drawing it:
 

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freak

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Actually what makes the beam itself visible is totally dependent on the particle in the air.
A laser is coherent light that travels in a straight line, so the only way you're going to see any beam from the side (light going perpendicular towards the side) is if the light is reflected off of some particle in the air.

For instance, a 5 mw laser in a fog or really smoky room will show the beam very easily, on the other hand if you were in an electronics clean room with perfectly or nearly perfect clean air that are free or particles, you could turn on a 10 Watt green laser in the dark and no beam would be visible at all; only the spot it produces at it's termination point.
So beam visibility cannot be used as a tool to tell you how much power you have, it's fully dependant on particles floating in the air.
You can however, compare two lasers side by side and the more powerful will be more visible, but without the particles there is nothing. So your laser may have a very bright beam one day and much less the next, it just depends on what's floating around.

Two questions...

1. So with particles held constant the only variable is power?

2. Why is green typically visible when red is not?
 
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At 90° you should (theoretically) see nothing. IRL it'll depend on power, wavelength, ambient light and as members said, particle size and transparency.

The answer to your second question is easily found with a google search: Key tags: wavelength, peak night vision
 
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Two questions...

1. So with particles held constant the only variable is power?

2. Why is green typically visible when red is not?


1. If particles in the air are constant, then power, wavelength and beam diameter are the variables.

2. The human eye has best response in the green range, red is much less, but a red laser can be very visible if more power is used.

Beam diameter is a factor in that a larger beam diameter will hit/ reflect off of more particles in the air and be more visible; but the larger beam diameter also means the light is less concentrated and would have lower burning ability.
 
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While you're 99.9% right so far, bootleg, the part about beam diameter is slightly inaccurate. The more concentrated the light, the more visible the beam. Therefore, an expanded beam would actually appear less bright than a thinner beam.

Also, with short wavelengths (blue or violet) the wavelength is small enough to cause light to be reflected from the molecules of the air itself. This is called Rayleigh scattering and is the reason that the sky is blue, and the reason why blue laser beams can be more visible than red even though the human eye perceives both with about the same sensitivity (theoretically, they should look about the same but blu-rays always have a more visible beam than red lasers for the same power output, even with few impurities in the air).. Also, blu-rays can cause some of the particles in the air to fluoresce, which enhances this effect..
 
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While you're 99.9% right so far, bootleg, the part about beam diameter is slightly inaccurate. The more concentrated the light, the more visible the beam. Therefore, an expanded beam would actually appear less bright than a thinner beam.

You'd think so, but in practice I've found that high powered greenies that get a wide beam diameter can be even more visible in some circumstances. And I think I know why.

As we've already established in this thread, seeing the beam is about hitting particles. When you're a thin beam you will hit fewer particles with higher power. But when you have a fat beam you hit more particles with less power. With a high powered greenie even with a fat beam you still have enough power to reflect off the particles, and since you're reflecting off more particles in a bigger area it's a lot easier to see.

Total speculation of course there.
 
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A beam of light will be the least visible when observed from an angle perpendicular to the beam path.
This is because there is not a lot of light reflected at this angle.
If you turn on your laser and shoot it down the hall, you will be able to see that when looking toward the source the beam will be brightest.
Looking from the source, the beam will still be bright, but the particles in the air will not be as noticeable.
As you increase the angle at which you are viewing the beam, it will gradually decrease in brightness until you reach the minimum visibility at about 90 degrees from the direction of the beam.
 
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You'd think so, but in practice I've found that high powered greenies that get a wide beam diameter can be even more visible in some circumstances. And I think I know why.

As we've already established in this thread, seeing the beam is about hitting particles. When you're a thin beam you will hit fewer particles with higher power. But when you have a fat beam you hit more particles with less power. With a high powered greenie even with a fat beam you still have enough power to reflect off the particles, and since you're reflecting off more particles in a bigger area it's a lot easier to see.

Total speculation of course there.

You may be right about that.. it does make sense, but I can tell you that with a laser projector, the beam is always brightest near the projector where the beam is still thin. As it diverges, it becomes less visible.
 
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Oh, you can't really do much with laser projectors in this sense. When it's up close to the projector then the beam isn't moving very fast, it stays in the same spot mostly. Where as when you get far away the beam is whizzing around at top speed, so it's in a certain spot less so is harder to see.
 
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I see what you're saying, but I'm not sure that accounts for all of the decrease in brightness. Even static beams have the same result. The wider the beam gets, the less visible it becomes. The concept of a wider beam intercepting more airborne particles could only be true up to a point, depending on power. With any visible laser, more power adds up to more visibility at any beam diameter.
 
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I think it's very much dependent on the conditions. Enough particles in the air with the right laser at the right beam thickness will appear brighter than a tighter beam. That's what I've found anyway. Most of the time it's not like that though.
 
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Scattering causes the side view of a laser beam. Shorter wavelength laser beam cause stronger scattering than longer wavelength laser beam.
 
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