Quick question about Rayleigh scattering:

[enigmahack]

I was reading up on exactly what Rayleigh scattering is, and it totally makes sense to me, and even explains why the sky is blue. It also explains why laser beams are easier to see when they're pointed towards you than from away from you, however they're still easy to see sometimes even from the side in a relatively dustless room.

It DOES make me wonder two questions:

Even though green is easier for us to see, would a blue laser potentially have a slightly "brighter" beam (When I say brighter, I'm not referring to our eye's ability to acknowledge the light, however the amount of photons that would be sent to our eyes) than alternate colors such as Red, Orange or Yellow?

Would you still be able to see a laser beam in a vaccum? If so, why?

I've been pondering these things for a little while now, trying to develop an answer and I think I do have a general idea, but I'm hoping that someone else's answer could help me better understand the physics behind Rayleigh scattering

Thanks in advance!

 

[Blord]

You said it yourself. We see laserbeam because laserlight scatters or reflected on particles, molucules, atoms etc in the air. In vacuum there is nothing for light to bounce off. So we can't see the beam in vacuum.

 

[enigmahack]

Yeah, I thought so, which makes sense... I just wanted to see if there was a consideration I might not have thought of that someone could interject with

 

[magonegro]

Even though green is easier for us to see, would a blue laser potentially have a slightly "brighter" beam (When I say brighter, I'm not referring to our eye's ability to acknowledge the light, however the amount of photons that would be sent to our eyes) than alternate colors such as Red, Orange or Yellow?

Would you still be able to see a laser beam in a vaccum? If so, why?

Answer to the first question:
Don't think only in the number of photons, but also its energy. Let's say you have a 1mw green and a 1mw blue, you will have less photons per second in the blue one, because the energy radiated is the same (1mw) but the energy of a blue photon is more than the green one. The Rayleigh scattering tells than a higher energy photon is more prone to interact with matter (assuming there are matter in the photon's way) due to its lower wavelength but we are talking about particles much little than the wavelength of the photon, let's say atoms and molecules; but not the macro-objects suspended in air like dust or snowflakes. Every beam, the green and the blue will be catched by these objects. Think like this: if all the atmosphere were full of dust heaven's color will be black. Rayleigh scattering have to be taken in mind but solid micro particles floating can make a great difference to every wavelength beam. Just take this into consideration.

More info: Mie theory

Answer to the second question:
See answer to first one.