Light one hundred times slower

A pair of physicists manages to reduce the speed of a laser pulse by passing the light through a photonic crystal.

Photonic crystal is a structure that controls light. For this it has numerous layers ordered periodically, of different dielectric constants. Thus, the ray of light, as it passes from one side to the other, finds a change of dielectric constant, which hinders, say, the trajectory of the luminous wave.

However, it must be clarified that two types of speeds are distinguished: on the one hand the phase speed – the speed of the wave – and on the other the group speed – the speed of impulse, that is, the speed of the rays of different wavelengths that go to the same pulse. What they have slowed down is group speed.