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Maxwell2D: Refractive index gradient

Dielectric constant distribution

This animation illustrates the propagation of electromagnetic waves in the presence of a gradient in refractive index. The bending of the wave is what happens in mirages, shimmering of the light over a hot surface and anomalous propagation of radar beams. In this case the beam also gets slightly focused, as shown by the time-averaged Poynting vector.
Wikipedia link: Refraction

Electric field animation

Time-averaged Poynting vector

This is an animation of the component of the electric field out of the plane of the page.The direction in which energy is travelling at any instant is proportional to the cross product of the electric and magnetic fields, known as the Poynting vector. The arrows show the direction of the Poynting vector averaged over the simulation, while the colours show its strength.