For example, with respect to an information recording medium, such as a Compact Disc-Read Only Memory (CD-ROM), a Compact Disc-Recordable (CD-R), and a DVD-ROM, there has been also developed an optical disc of a multilayer type in which a plurality of recording layers are laminated on the same substrate. More specifically, a dual-layer type optical disc has a first recording layer which is on the nearest side viewed from the irradiation side of laser light in recording by an information recording apparatus (i.e. on the closest side to an optical pickup). The first recording layer is referred to as a “L0 layer”, as occasion demands. Moreover, it has a semi-transparent reflective film located on the rear side of the first recording layer (i.e. on the farther side viewed from the irradiation side of the laser light). The dual-layer type optical disc has a second recording layer which is located on the rear side of the semi-transparent reflective film via a middle layer, such as an adhesion layer. The second recording layer is referred to as a “L1 layer”, as occasion demands. Moreover, it has a reflective film located on the rear side of the second recording layer.
The information recording apparatus, such as a CD recorder, for recording record information onto the dual-layer type optical disc, uses an irreversible change recording method or a rewritable method by heat, by focusing (or irradiating) the laser light for recording on the L0 layer or the L1 layer.    Patent document 1: Japanese Patent Application Laying Open NO. 2000-311346
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