An optical pickup apparatus comprises: a first light source for emitting a first light flux; a second light source for emitting a second light flux; a third light source for emitting a third light flux; and an objective optical element. The objective optical element comprises an optical surface comprising a central area and a peripheral area. The central area comprises a first optical path difference providing structure, and the peripheral area comprises a second optical path difference providing structure. The objective optical element converges the third light flux which passes through the central area of on the third optical disk. The objective optical element converges the first and second light fluxes which pass through the peripheral area on the first optical disk. Each of the first and second optical path difference providing structures comprises a predetermined basic structure.

 
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> Apparatus and method for detecting surface defects on a workpiece such as a rolled/drawn metal bar

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