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A glide height tester for inspecting a surface of a spinning magnetic disk includes a glide plate, which is mounted to pivot above the disk surface. A reflective surface fastened to the glide plate is imaged by interferometric apparatus which produces a calculated output indicating a first angle of

A glide height tester for inspecting a surface of a spinning magnetic disk includes a glide plate, which is mounted to pivot above the disk surface. A reflective surface fastened to the glide plate is imaged by interferometric apparatus which produces a calculated output indicating a first angle of the glide plate. The interferometric apparatus includes a Wollaston prism, which can be rotated 90-degrees to provide an output indicating a second angle of the glide plate, perpendicular to the first angle.

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Inspection apparatus for inspecting a surface of a disk, wherein said apparatus comprises: means for rotating said disk about a center thereof; a glide plate movably mounted to extend adjacent said surface of said disk, wherein air dragged by rotation of said disk causes movement of said glide plate

Inspection apparatus for inspecting a surface of a disk, wherein said apparatus comprises: means for rotating said disk about a center thereof; a glide plate movably mounted to extend adjacent said surface of said disk, wherein air dragged by rotation of said disk causes movement of said glide plate; a reflective surface mounted to move with said guide plate; and optical means for measuring rotation of said reflective surface in a first pivoting direction wherein said optical means comprises: a laser producing a coherent, linearly polarized beam; optical apparatus, wherein said coherent, linearly polarized beam is decomposed into first and second projected sub-beams, with said first projected sub-beam being linearly polarized in a first direction, with said second projected sub-beam being linearly polarized in a second direction, perpendicular to said first direction, wherein said first projected sub-beam is projected to a first test spot on said surface under test, wherein said second projected sub-beam is projected to a second test spot on said surface under test, with said first and second test spots extending along said surface under test in a spaced-apart relationship, wherein said first and second projected sub-beams, after reflection from said first and second test spots, are recombined into single, elliptically polarized return beam; a polarizing beamsplitter in which said elliptically polarized return beam is split into a first return sub-beam polarized in a third direction and a second return sub-beam, polarized in a fourth direction, perpendicular to said third direction; a first photodetector measuring intensity of said first return sub-beam; and a second photodetector measuring intensity of said second return sub-beam; wherein a portion of said optical means is rotatable about an optical axis extending perpendicular to said reflective surface to measure rotation of said reflective surface in a second direction, perpendicular to said first pivoting direction.