| 摘要 |
PURPOSE: To enhance the defect inspection sensitivity by specifying the sum of angles with respect to first and second reference directions and the maximum Faraday rotational angle of a Faraday effect element. CONSTITUTION: When the polarity of magnetization is positive, the lights from LEDs LA1,..., pass through polarizing plates FA1,..., to produce linearly polarized lights in the direction of +30 deg.. When the polarity of magnetization is negative, the lights from LEDs LB1,..., pass through polarizing plates FB1,..., to produce linearly polarized lights in the direction of -30 deg.. The light impinges on a Faraday effect element 21 and turns by±15 deg. within the element 21 depending on the direction of magnetic field at a position where the magnetic field is present in the vertical direction. Consequently, the reflected light is linearly polarized in the directions of +45 deg. and +15 deg. at the time of positive polarity and in the directions of -45 deg. and -15 deg. at the time of negative polarity. At a position where the magnetic field is not present in the vertical direction, the reflected light is polarized in the directions of +30 deg. and -30 deg.. Since an analyzer 31 has a polarizing direction of +45 deg., the reflected light is energized or deenergized depending on the sign of polarity. Since the optical image received by a camera 32 is brightest at +45 deg. and a component corresponding to a defect includes polarized components of±45 deg., the contrast is high enough to facilitate detection of defect.
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