Magneto-optical disk
<hardware, storage> Plastic or glass disks coated with a compound (often TbFeCo) with special properties.
The disk is read by bouncing a low-intensity laser off the disk. Originally the laser was infrared, but frequencies up to blue may be possible; the shorter the wavelength the higher the possible density.
The polarisation of the reflected light depends on the polarity of the stored magnetic field.
To write, a higher-intensity laser is used to heat the material up to its Curie point, allowing its magnetisation to be altered and "frozen" as it cools.
Storage FAQ (http://www.cis.ohio-state.edu/hypertext/faq/usenet/arch-storage/part1/faq.html).
