Dissipation of Light: Measuring Intensity & Energy Loss

[linearmot]

Hi,

I´m trying to figure out how light intensity diminishes when traveling through air. I assume absorption/scattering are responsible. But how far can a single light ray travel, and what mechanisms are in place that causes light to lose its energy. I´m trying to come up with a relationship rather than estimates.

Thank you.

 

[Born2bwire]

I think the best you can hope for is just estimates. What you are talking about is a statistical phenomenon. It all depends upon the density and composition of your gas and the various paths that the light follows. In the end, the best you can hope for is a statistical expression of the behavior that would bear out only for a large sampling.

The primary means of scattering in air is generally Rayleigh scattering. There will also be a very minute amount of Raman scattering. Finally, large dust particles in the air would probably cause Mie scattering. Most of these mechanisms do not give rise to a loss of energy. Rayleigh and Mie are elastic and so conserve energy but Raman scattering is a lossy process as the frequency of the light changes. For the most part we would probably just define a loss factor to the gaseous medium as a whole and use that the find the overall attenuation as a function of path. But this would probably be a small factor when compared to the loss of intensity observed due to scattering.