Produced by solving the wave equation on a computer.
a) Reflector with a gap - Huygen's principle. Only part of the wavefront gets through the gap. The energy that gets through the gap spreads spherically in the lower part of the box.
b) Half-width reflector - Edge diffractions. On the left (reflected) side, the wavefront gets reflected (with negative amplitude). On the right side, the wavefront continues on its way. Energy is scattered from the edge of the reflector, causing both incident and reflected energy to spread spherically from this point.
c) Isolated object - Wavefront healing. The wavefront is diffracted around the object, and some distance later the wavefront has 'healed' back to almost its original form, making it difficult to detect the object.
a) Less than critical angle. Most of the wavefront penetrates the interface and is 'bent' according to Snell's law. A fraction of the wavefront is reflected.
b) Critical angle. Wavefront in the lower layer is vertical (ideally- the simulation is not perfect). Reflection is strong.
c) Greater than critical angle. Wave is completely reflected from the interface. Mulpile reflections are built up as it travels down the box.