Importance

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Abstract

A system is disclosed for detecting local surface discontinuities in magnetic data storage disks. The system includes a spindle that rotatably supports a magnetic disk being tested. An interferometer generates a laser beam which is guided through an optics assembly supported above the magnetic disk, for linear movement radially of the disk. The combined radial and linear movement causes the laser beam to trace a spiral scanning path on the disk surface. The disk surface scatters the laser energy, a portion of which is returned to the interferometer and caused to interfere with a reference beam. The resulting interference intensity fluctuates in response to changes in the optical path length, thus measuring topographies of the discontinuities. A discontinuity recognition triggering pulse can be positioned in time with respect to indexing pulses, to identify the location of the associated discontinuity radially and angularly of the disk. The triggering pulses limit the storage of scanned surface data to the part of the data that locates and characterizes discontinuities exceeding a predetermined size threshold.

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First Claim