Subject: Laser distance-diffusion equation when related to output power?

Howdy,

Is there a diffusion equation that would correlate the power output of a given 
laser to the distance it will travel before dispersing? Basically, I'm 
wondering if I'm given the power rating of a laser (low power, .5mW-5mW) and 
thw wavelength at which it operates (~632 nm), how am I able to tell the 
distance it will be able to travel before becoming unnoticable. Also, what if I 
were to pass it through something less transparant than air- ie. typical 
special effects smoke, from a smoke machince so the laser'll be visable 
throughout its path? Thanks for your time!

Clay

Re: Laser distance-diffusion equation when related to output power?