Which laser goes the furthest? A response...

I edited my post to indicate I was referring to the beam of a 4 watt 470 nm and 1.3 watt 520 nm green pointers into the night sky. Side by side, I didn't see much difference in brightness of the beam, but 77% is so close, I didn't expect to.

paul1598419 said:

One thing I found to be in disagreement with Rayleigh scattering of sunlight through the atmosphere is due not to aerosols, but molecular gases such as N2 and O2. These molecules have a length that cause scattering of short wavelength light causing the sky to look blue, and at dusk or dawn to look more reddish. Apparently aerosols cover a large volume in particulate matter from NO2 to bits of dust which are enormous on a molecular scale. I think most people here are aware of the ability of dust particles to scatter laser light in the visible spectrum. These are more likely indoors, except where smog is concerned in areas where air currents aren't available to carry them off quickly enough to keep them from becoming visible.

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Yes, you're right/correct. of couse, N2 being 77-78% of the atmospheric gas. Blue wavelength is ~450 nanometres or 0.45 thousandths of a mm. Air molecules, mostly nitrogen and oxygen, are 1000X smaller still. They interact only very weakly with visible light but with their enormous numbers in the atmosphere we see the effects.

I think the guy from the RASC Calgary Centre who did that article meant for particles in the sense of particles smaller than the wavelength, particles include molecules or atoms. At least that what I took him to mean. Aerosols are another component . Is a more complicated thing that that artiicle bothered to mention--they just said Rayleigh Scattering allows beam visibility amd makes sky appear blue. Releigh Scattering is from molecules of gas and other small particles that scatter light within the atmosphere water, dust, and aerosols that cause a defined polarization pattern.
Rayleigh scattering is due to the electric polarizability of the particles which is wavelength dependent.
When the electric field of a light wave acts on the charges within a particle, it causes them to move at the same frequency. becoming a small radiating dipole whose radiation we see as scattered light. Wavelength dependence of scattering means that shorter (blue) wavelengths are scattered more strongly more than longer (red) wavelengths(example 400nm is scattered ~10X more strongly than 700nm) in the Rayleigh limit.. Scattering being inversely proportional to the fourth power of wavelength so the sky looks a shade of blue--really it is a mix of all the scsttered colors but mainly blue and green so looks blue and the yellow color of the sun is due to the colors not scattered away, the longer wavelengths being seen seen directly giving the sun it's yellowish color. In outer space the the sky is black and the sun is white.

Then there is haze aerosol component of how the sky looks due to particles suspended in the molecular gas. Mie scattering coincides with Rayleigh scattering in the special case where the diameter of the particles is much smaller than the wavelength of the light; in this limit, however, the shape of the particles no longer matters. These particles are typically much bigger than molecules, and Mie scattering explains the scattering behavior of these particles. Because the haze particles typically scatter more uniformly than molecules for all wavelengths, haze causes a whitening of the sky. The actual particles comefrom many sources – volcanic eruptions, forest fires, cosmic bombardment, the oceans – and it is very difficult to precisely characterize the haze of a given sky.

Anyway we are a bit beyond CIE table values based Relative Wavelength Brightness Calculator --The calculators set of colour-matching functions being only representative of the colour-matching properties of observers with normal colour vision for visual field sizes of angular subtense from about 1° to about 4°, for vision at photopic levels of adaptation.

Yes, and clouds scatter all wavelengths of light giving a white or grey color to them. IIRC, it's because of the difference in partical size that causes this.

paul1598419 said:

Yes, and clouds scatter all wavelengths of light giving a white or grey color to them. IIRC, it's because of the difference in partical size that causes this.

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Yes, exactly.
A good example of white light reflected by high density of particles in the air is sunlight shining into St Peter's Basilica in the picture below.
You see something like this outdoors as well when sunlight shines through breaks or holes in clouds and sunbeams called "crepuscular rays" occur.

That's a nice example of this scattering effect.

If they thought about it, they could have designed the top so the light streams produce something really cool looking which has some kind of religious representation to spirit or something.

good info Alaskan :topic:
405 nm blue-violet: 1% as bright (Not UV, but not far from it).
450 nm blue: 10% as bright
465 nm blue: 14% as bright
470 nm blue: 17% as bright
520 nm green: 88% as bright
638 nm red: 10% as bright
650 nm red: 5% as bright
660 nm red: 2% as bright
670 nm red: 1% as bright (Not IR, but not far from it).
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If 520nm is 88% bright then what wavelength is 100% bright (532nm) ?

It is 532.

Alien Laser said:

good info Alaskan :topic:
405 nm blue-violet: 1% as bright (Not UV, but not far from it).
450 nm blue: 10% as bright
465 nm blue: 14% as bright
470 nm blue: 17% as bright
520 nm green: 88% as bright
638 nm red: 10% as bright
650 nm red: 5% as bright
660 nm red: 2% as bright
670 nm red: 1% as bright (Not IR, but not far from it).
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If 520nm is 88% bright then what wavelength is 100% bright (532nm) ?

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555.5 nm has the apparent highest brightness.

Whilst this is true Steve, the value that 520's beam is 88% as bright of is 532 according to that calculator.
I at first answered 555nm as well. But then I went back to check.