Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation; by modifying optical properties or the physical structure; , reproducing using an optical beam at lower power; by sensing optical properties; Record carriers therefor
with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
