LASER RECORDING SYSTEM USING PHOTOMAGNETICALLY MAGNETIZABLE STORAGE MEDIUM

摘要

An optical coherent light data recording and reading system utilizing an erasable and/or permanent recording medium. The recording medium is formed of a layer of substantially transparent photomagnetically responsive magnetizable material having a anisotropic optical response under magnetization coated on a substrate or carrier. The substrate may have a reflective surface or a thin reflective metal layer may be interposed between the substrate and the layer of magnetizable material. A polarized beam of coherent light generated by a laser in a wavelength suitable for optical pumping of exchange resonance spinwave modes of the magnetizable material is focused by an optical recording head onto the photomagnetically responsive layer of magnetizable material in a diffraction limited spot size. Optical pumping is achieved by either parametric excitation or quantum-mechanical excitation. The laser beam and recording medium are translated relative to each other and the rate of translation and laser intensity are adjusted so that the thermal temperature developed in the layer of magnetizable material is less than the Curie temperature of the material during recording. The recording laser beam is optically modulated to induce localized photomagnetization along the recording medium to thereby provide remanent tracks of variable birefringence in the magnetizable material as a function of a signal to be recorded. Readout is accomplished with a reading laser by means of the Faraday effect. Preferably optical recording takes place in the spectral region of maximum absorption efficiency by the exchange resonance modes of the recording material while optical readout takes place in the spectral region of maximum Faraday rotation. Ramanent data tracks are erased by secondary scanning of the recording laser at an intensity and/or scanning rate sufficient to heat the record material above the Curie temperature.