| 摘要 |
PURPOSE:To improve stability of magnetic bits and to prevent information being erased that must not be erased by causing change in quality of the recording layer of the optical/magnetic recording disc for the information recording purpose and detecting changes in reflectance of recording bits of the optical/ magnetic recording disc for the reproduction puropose. CONSTITUTION:An energy at higher level than for normal writing is used to damage the recording medium to such a degree as to cause a change in quality. The recording layer of optical/magnetic recording discs usually consists of an amolphous magnetic film which can be partly or completely crystallized by applying an light energy at a higher level than in normal use to the recording layer. Thus crystallized bits are difficult to return to original amolphous state, and therefore difficult to erase and stable over along period of time. The abovementioned change in quality of the recording layer is caused by the thermal energy derived from a light energy, and an external magnetic field is not always required for this purpose.
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