| 摘要 |
PURPOSE:To attain the reduction in the cost of the titled apparatus, by constituting said apparatus so that all of condensed luminous fluxes by a hologram are detected by the light detector having a specific diameter arranged so as to provide a predetermined distance from a recording medium in which a hologram having light condensing action was recorded. CONSTITUTION:The coherent beam 2 from a semiconductive laser 1 is focused onto the recording surface of an optical disc 5 through a beam splitter 3 and a lens 4, and the reflected beam is reflected by the beam splitter 3, through the lens 4 to be incident on a beam detector 7 through a recording medium 6 in which a hologram was recorded. In this case, the detector 7 is arranged at the position in the vicinity of the focus point of the medium 6 and the diameter thereof is set to one equal to and more than the max. diameter by the variation in a wavelength among diameters possessed at said position by condensed luminous flux. By this method, all of beams 2 can be detected by the detector 7 in spite of the variation in a wavelength. |
