| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to improve an overwriting erasure ratio by irradiating a crystal space part with a laser beam of a first power level, then irradiating the same with a laser beam of a second power level different from the first power level at the time of forming the crystal space part. SOLUTION: The crystal space part is formed by irradiating this part with the beam formed as pulses between the peak level (Pc1) lower than the recording power level for making a recording layer amorphous and a bottom power level (Pc2) lower than the Pcl. At least either of the pulse of Pc1 and the pulse of Pc2 is shorter than the time when the full-width at half value of the laser beam passes one point above the medium. The pulse lengths of Pc1 and Pc2 are otherwise at least shorter than the time corresponding to the shortest mark space length. The level of Pc1 is so set as to attain the temperature at which the crystal growth rate of the recording layer is remarkable. The level of Pc2 is so set as to attain the temperature at which the crystal nucleus forming frequencies of the recording layer are remarkable.
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