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Homework Help: Cross section - scattering of light by light

  1. Sep 30, 2011 #1
    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!
  2. jcsd
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