1. The problem statement, all variables and given/known data Red and green laser (wavelength of 650 nm and 532 nm respectively) are directed towards each other at 20 degrees. Each laser has 5 mW power, with diameter of 1mm. Assuming the intensity of the beams are decreased by 10% each after the 'collision', estimate the upper limit on the cross section, σ, for the scattering. 2. Relevant equations σ = 0.1*(NRED + NGREEN) / (NRED + NGREEN)*π*0.0005^2 where N is the number of photons per second N = 5e-3 / (hc/λ) 3. The attempt at a solution I'm just unsure whether the equation I used for σ is correct or not. Can somebody confirm? Many thanks in advance!