Because the reflectivity of the material at the melted state is often much lower than at the solid state, the rear part of the laser spot can be effectively
masked by the phase-changed layer, which is equivalent to a spot size reduction.
In principle, the size of the aperture can be controlled by modulating the laser
intensity. When an aperture with a diameter smaller than the diffraction limit is
formed, marks smaller than the diffraction limit can be recorded/read out combined
with the near-field effect. The low optical throughput still seems to be a technical