FOCUS DISPLACEMENT DETECTION DEVICE OF LASER BEAM, AND FOCUS DISPLACEMENT ADJUSTMENT METHOD OF LASER BEAM

摘要

PROBLEM TO BE SOLVED: To highly accurately detect displacement among focus positions of a plurality of laser beams without raising cost, and to highly accurately control focus positions of the plurality of laser beams.

SOLUTION: A focus displacement detection device is provided with: a reflectance variable object wherein reflectance of a laser beam focused position is changed; a driving means for driving a table setting the reflectance variable object or an optical head so that the focused position of the laser beam is moved in an optical axis direction of the laser beam relatively to the reflectance variable object; a laser beam irradiation means for irradiating the reflectance variable object with a designated laser beam with intensity by which reflectance is changed and irradiating the reflectance variable object with the other laser beam with intensity by which reflectance is not changed; a peak value acquiring means for acquiring a peak value of a signal for adjustment prepared from a photo detection signal of a photodetector of the optical head; and a detection means for detecting the displacement of focus positions between the designated laser beam and the other laser beam based on the acquired peak value.

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