Light emitted from a laser is divided into two light waves so that the ratio
of the power of one light wave to the power of the other will be appropriate. The
resultant light waves are irradiated to the same track on a medium. The preceding
spot is used for erasure, and modulated so that the same pattern as the one formed
with a recording pulse will be formed. The high-power component of the modulated
light of the erasing spot causes the temperature of a recording layer to be equal
to or higher than the melting point. The medium-power component of the modulated
light forms a crystallizing temperature area on the recording layer. A liquid crystal
diffraction grating is used to divide power, and a power division ratio is variable
and controllable.
