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Maxwell2D: Diffraction grating, low frequency

Dielectric constant distribution

A diffraction grating diffracts light by an angle that depends on its wavelength. It consists of a series of equally spaced groves of a similar spacing as the wavelength of the radiation. The simplest way to understand how it works is using Huygens' Principle; each grove acts like a separate source of electromagnetic waves, but the phase of each is offset from that of its neighbours to a degree that depends on the angle of the grating with respect to the incident ratiation. The diffraction angle is that which results in a constructive interference between all the different sources. The sources also combine constructively in the direction of the incident radiation.
Wikipedia link: Diffraction grating

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.