| 摘要 |
PURPOSE:To perform rewriting of information, by using a recording film utilizing reversible phase change and erasing information by projecting high-power light and, after the power of the light is reduced by a period which is shortened when the projecting time for erasing, increasing the power of the light again. CONSTITUTION:When a high-output beam is projected on the already recorded part of a required section and, after a molten state is once passed, erasing (cooling) is performed for a short time while a recording medium is rotated and the intensity of laser light is maintained at its reading-out output level, most of the records in the part are erased. The state of erasing depends upon the ratio of the cooling time to the crystallizing time. The crystallizing time (r) is determined by the characteristic of a recording film and the cooling time is determined by the relative velocity V between the recording medium and the light spot. The radius of the area which can reach the temperature, at which high-speed crystallization takes place, of the recording medium is within a range of ar (0<=a<=1) and the time, during which the temperature becomes lower than the temperature at which high-speed crystallization becomes possible, when the light spot passes at the velocity V is ar/V. Therefore, when the light is turned off or the projecting power of the light is lowered by a time t ar/V, one-beam overwrite with no erasing omission can be carried out. |
