| 摘要 |
PURPOSE:To perform an economical scan with high accuracy, by providing a conductive film to a hologram disk, detecting the surface deflection of the hologram disk from the electrostatic capacitance between the conductive film and an electrode opposite to the conductive film and controlling the incident angle of an incident beam in accordance with the degree of the above-mentioned surface deflection. CONSTITUTION:An electrode 16 is set at the position opposite to a conductive film 5 with aluminum vapor deposition which is formed on the back side of a hologram disk 1. The electrostatic capacitance of the electrode 16 is detected by a displacement measuring circuit 17. The output of the circuit 17 is fed to a frequency controlling circuit 18 and oscillates an AO (audio-optic) modulation driving frequency. An AO modulation driving circuit 19 modulates the AO driving frequency based on the modulating signal given to a modulation input terminal 20 and then drives an AO modulator 10. Thus the primary diffraction angle theta is varied for the beam given from a gas laser 8, and compensation is carried out in response to the degree of surface deflection of a disk 3. As the modulator 10 is used also to control the angle of the incident beam, an economical scan is carried out with high accuracy. |
