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A system (300) for gating a sensor (118) includes a detector (120) that detects light and outputs a signal (102) corresponding to the light. A control unit (334) receives the signal (106), and enables and disables a power supply (314) in response to the signal (106) to generate a gated power signal

A system (300) for gating a sensor (118) includes a detector (120) that detects light and outputs a signal (102) corresponding to the light. A control unit (334) receives the signal (106), and enables and disables a power supply (314) in response to the signal (106) to generate a gated power signal (316). The power supply (314) outputs the gated power signal (316) to a sensor (118) sensing the light.

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A system (300) for gating a sensor (118) includes a detector (120) that detects light and outputs a signal (102) corresponding to the light. A control unit (334) receives the signal (106), and enables and disables a power supply (314) in response to the signal (106) to generate a gated power signal

A system (300) for gating a sensor (118) includes a detector (120) that detects light and outputs a signal (102) corresponding to the light. A control unit (334) receives the signal (106), and enables and disables a power supply (314) in response to the signal (106) to generate a gated power signal (316). The power supply (314) outputs the gated power signal (316) to a sensor (118) sensing the light. t beam from a second one of the light sources, spherical aberration is corrected by the diffractive optical element for the portion of the light beam passing through the first portion of the convex lens. 5. The optical pickup device as claimed in claim 4, wherein the convex lens is made of a synthetic resin, the diffractive optical element is a blazed-shape hologram provided at least on one surface of the convex lens, and a plus-first-order diffracted light or a minus-first-order diffracted light of the hologram is used to cancel the spherical aberration generated by a change in the refractive index of the synthetic resin material forming the convex lens due to a temperature change. 6. The optical pickup device as claimed in claim 2, wherein the diffractive optical element is a hologram having a blazed shape and has a first-order diffraction efficiency of 75% or higher whether the wavelength of the light beams emitted from the light sources is a first wavelength λ1 or a second wavelength λ2. 7. The optical pickup device as claimed in claim 6, wherein the first-order diffraction efficiency of the diffractive optical element with respect to the light beams with the first wavelength λ1 and the second wavelength λ2 is 90% or higher. 8. The optical pickup device as claimed in claim 2, wherein the diffractive optical element is a blazed-shape hologram. 9. The optical pickup device as claimed in claim 8, wherein the direction of inclination of the blazed shape is such that the height is lower on the outer side than on the center side of the objective lens. 10. An optical pickup device comprising: two light sources for emitting light beams with different wavelengths; an objective lens for condensing the respective light beams emitted from the respective light sources onto a signal recording surface of a first or second optical recording medium via a respective transparent cover layer provided on the optical recording medium; a light beam branch element for branching a light beam reflected by the signal recording surface from optical paths returning to the light sources; and a photodetector for receiving the light beam branched by the light beam branch element; wherein the objective lens has a convex lens and a diffractive optical element provided on at least one surface or in the vicinity of the convex lens, and condenses diffracted lights of the same order generated by the diffractive optical element, of the two light beams with different wavelengths emitted from the respective light sources, onto the signal recording surface, thereby condensing the respective light beams onto the signal recording surface in the state where spherical aberration generated in the transparent cover layer is corrected; wherein the light sources emit a light beam with a first wavelength λ1 and a light beam with a second wavelength λ2 longer than the first wavelength λ1, respectively, the numerical aperture of the objective lens with respect to the light beam with the first wavelength λ1 is a first numerical aperture NA1, the numerical aperture of the objective lens with respect to the light beam with the second wavelength λ2 is a second numerical aperture NA2, the thickness of the transparent cover layer corresponding to the light beam with the first wavelength λ1 is a first thickness t1, and the thickness of the transparent cover layer corresponding to the light beam with the second wavelength λ2 is a second thickness t2 greater than the first thickness t1, wherein when the wavelength of the light beam is the first wavelength λ1 and the numerical aperture is the first numerical aperture NA1, the spherical aberration in the case where the thickness of the transparent cover layer is the first thickness t1 is corrected to not more than λ/100 RMS by a first-order diffracted light diffracted by the diffractive optical element, and wherein when the wavelength of the light beam is the second wavelength λ2 and the numerical apertu