| 摘要 |
PURPOSE:To obtain always the suitable number of the aperture by providing the aperture number variable means to lie between the optical system and the recording media and change the number of the aperture, and the shifting means to shift the aperture number variable means along the light path. CONSTITUTION:When recording is executed by making a fine hole on an optical disk 5 by melting and vaporizing with a laser beam, an energy much larger than the energy of the laser beam at the time of reproduction is necessary, and therefore, the number of the aperture of the optical system is made large, the spot diameter of the laser beam collected on the optical disk 5 is made small and the density of the laser beam is made large. Namely, by shifting an aperture number variable lens 8 in the light path direction of the laser beam with an aperture number variable lens shifting actuator 9 to input an aperture number variable lens 8, an interval l between a movable lens 4 and the aperture number variable lens 8 is made small, the focus distance is made small, the number of the aperture is made large, and thereby, the spot diameter is made small. Thus, the optimum number of the aperture can be obtained. |
