| 摘要 |
PURPOSE:To reproduce data stably and with high precision by making the intensity distribution of beam which has passed through a phase plate nearly constant so as to provide an interference pattern which changed little even if the irradiated position of beam deviates. CONSTITUTION:The light beam going out of a laser 12 is made to parallel beam by collimator lens 14 and then enters a phase plate 16. The beam which has passed through the phase plate 16 is nearly constant in intensity distribution independing on the distance from a center point and enters an objective lens 22. The objective lens 22 radiates the incident beam on a mark set 28 consisted of two openings 26 provided on a recording medium 24 at a specified interval. The light beam which has passed through the openings 26 is converged by a condenser lens 30 and then made incident on a detector 32 so as to obtain an interference pattern. Based upon this interference pattern, the data which has been recorded as a mark interval of the mark set 28 is reproduced. |
