Regardless of computational cost, light is a kind of electromagnetic wave, so it can be simulated with Maxwell's equations. If we want to simulate light with Maxwell's equations, we need to express the electric field vector of light source with a formula.
If the light source is polarized, this task won't be hard, but what if I want to simulate natural light: to be precise, unpolarized light?
Is there any approximate formula for it?
If the final result I want to get is just light intensity, can I simply replace the unpolarized light source with a polarized one?
Well, to be honest, this question came to my mind when I read a paper that simulate light in a nanometric optic probe with Maxwell's equations and the incident light in that paper is polarized, I just want to know if unpolarized light is also available for Maxwell's equations.
Answer
To simulate unpolarized light, you need to do two separate simulations using Maxwell's equations.
In the first simulation, assume the incoming light has some polarization (any polarization will do). In the second simulation, assume that the light has the opposite polarization (y is opposite to x, right-circular-polarized is opposite to left-circular-polarized, etc.).
Now imagine that at every moment, randomly, the light is switching back and forth between these two simulations, too fast to measure. So the intensity for unpolarized light is the average of the intensity in the two simulations, the optical force is the average of the forces in the two simulations, etc. etc.
For more details see this answer and comments: https://physics.stackexchange.com/a/31975/3811
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