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Consumer Electronics by S. P. Bali

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MAGNETO-OPTICAL MATERIALS

Amorphous magnetic gadolinium–iron–cobalt compounds have been known for a long time. A laser beam can be used to heat the material locally, reverse the polarity of small areas and freeze it in this state. This technique makes it possible to write on a magnetised layer in a pattern of areas of opposite magnetisation directions. This type of pattern can then be read out with polarised laser light. The direction of polarisation of the reflected light is rotated slightly with respect to the polarisation of the original laser beam as a result of the Kerr effect. The written areas on the disc can, therefore, be distinguished from the unwritten areas and information can be read out. The information can be erased just as easily ...

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