Improved methods of direct overwrite in magneto-optical recording media

Two improved methods of achieving direct overwrite without a pulse magnetic field to write or erase domains are described. Both were demonstrated in special single-layer magnetooptical media with a compensation point of 125-30 degrees C and a Curie temperature of about 310 degrees C. One of these methods uses two laser beams at different power levels. The first beam is set at a low power level which is adequate for erasure but not for writing. This is possible because the laser energy required for erasure of written domains does not overlap with that for writing. The second beam is then fired at the higher pulse power required for writing to put in the new data. The second method uses only a single laser beam in which the pulse energy of the laser is modulated between a low level for erasure of previously written domains and a higher level for writing of new domains, directly overwriting the old data. Both methods have been experimentally demonstrated for variable-length domains so that the use of pulse-width modulation codes is possible. Scanning speeds as high as 15 m/s have been demonstrated.<
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