| 摘要 |
PROBLEM TO BE SOLVED: To provide a hologram element capable of efficiently utilize short wavelength light and to provide an optical pickup device capable of detecting the short wavelength light. SOLUTION: This device is provided with a first light source 1 which outputs light for reproducing a first information recording medium having a first wavelength, a second light source 2 which outputs light for reproducing a second information recording medium having a wavelength longer than the first wavelength, and a transmission type hologram element 4 which is provided in the outward light paths from the first and second light sources 1, 2 and is common to the first and the second light sources 1, 2 to obtain separate diffracted light fluxes separated from the outward paths corresponding to the returning fluxes from the first and second information media. The hologram 4 has a characteristic that the light for reproducing the first information recording medium has a larger product of diffraction efficiency related to the transmitting light flux through the hologram element 4 in its outward light path and the diffraction efficiency concerning the separately diffracted light flux, compared with the light for reproducing the second information recording medium. |
