Right as rain: Light encountering a raindrop with index of refraction

This variant of the video shows a linear wave reaching a circular area in which the speed of propagation is reduced to 75% of its value outside, which corresponds to an index of refraction of 4/3, as for water. The theory says that the part of the wave reflected backwards on the inside of the drop has maximal intensity at angles between about 41° and 42°. I think what we see on the simulation looks about right in that respect. The colors show the energy density of the wave (obtained by adding squares of the time-derivative of the wave height, and the wave speed times the norm of their spatial gradient). There are absorbing boundary conditions on the sides of the domain, which however don't work perfectly, which is why you see some waves reflected from the boundary. Music: “Pouring Out“, by Asher Fulero@Asher Fulero See also for more explanations (in French) on a few previous sim