| 摘要 |
PURPOSE:To enable to conduct whitening-signal recording at low frequencies and reduce noise components such as incompletely erased signals by a method wherein a recording medium preliminarily blackened to a saturation level is irradiated with a laser spot beam with a reduced modulation duty to produce a record on the medium. CONSTITUTION:A recording film 3 having such properties that the optical density is increased by gradual heating after heating and is decreased by rapid cooling after heating, it formed on a heat-resistant substrate 2 and it is heat-treated to blacken it to the saturation level, thereby obtaining a black disc 1. In the case of low frequency repetition, the duty of information signals 6 mudulating directly a semiconductor laser 4 is reduced, whereby the surface of disc is exposed to short pulses and the rapid cooling is made possible, so that the white-signal recording can be conducted. When erasing the recorded signals by blackening, the irradiating power is lowered and disc is irradiated with continuous light beam, whereby white bits are blackened and therefore the recorded signals are erased. |
