Writing Optical Fields: An Explanation by Niles

AI Thread Summary
The discussion centers on the representation of optical fields in the context of Maxwell's Equations and the dipole approximation. Niles questions the neglect of the spatial part in the expression for the electric field, specifically why it can be omitted when the dielectric function is time-invariant. The key point is that the spatial component does not influence the Hamiltonian of the system, allowing for its simplification. The context of the dipole approximation, where the atom's position is set to zero, further clarifies this approach. Understanding these principles is essential for accurately describing optical fields in various physical systems.
Niles
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Hi

When the dielectric function of a system is time-invariant, solutions of Maxwell's Equations are separable and they are usually written as (I only write the E-field)
<br /> E(r, t) = E(r) \exp(-i\omega t)<br />
Now, in my book they write an optical field as
<br /> E(t) = E_0\exp(-i\omega t) + E_0^*\exp(+i\omega t)<br />
Taking the real part of the two expressions, the time-dependence will be the same to a multiplicative factor, so all OK there. But why is it that I am allowed to neglegt the spatial part in the second way of writing the field? Is it simply because the spatial part is not a part of my Hamiltonian for the system?

Any help is appreciated.Niles.
 
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The context I read it in was regarding the dipole approximation, so that explains it (we set the position of the atom R=0).
 
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