| 摘要 |
PURPOSE:To obtain an optical system which will not require an automatic focusing mechanism by employing a head where a distance between an objective lens and a recording medium will not change even if a mirror for scanning a beam acts. CONSTITUTION:The recording medium has at least two types of crystal structures in the solid state, holds the crystal structure inherent to one temperature area in the other one, and/or composed of metal or alloy causing different volume changes in the crystal state. Namely, a beam spot is formed by using a light beam from a light source by means of a movable mirror and the objective lens on said information recording medium available from processing the reversible material, whose optical density is changed by heating and quenching and is returned again by heating and annealing, in a tape-like shape. In this case the tape shape is made arc-shaped so that the beam spot can be formed on the recording medium without fail even if the movable mirror is shifted, and the rotational center of the movable mirror is aligned with the center of the arc. |
