A laser based inspection tool (LIT) for inspecting planar surfaces is
described. In a preferred embodiment the LIT can simultaneously inspect
both planar surfaces of disks for use in disk drives. In one embodiment of
the invention, the incident beam is directed onto the surface to be
inspected at an angle slightly offset from perpendicular so that the
reflected beam is physically separated from the incident beam. The
reflected beam is routed to a detector which converts the intensity of the
reflected into an analog signal. The analog signal is sampled and
digitized to generate pixel data stored in a buffer. Various analyses are
performed on the data including calculating a rate of change in the pixel
data. If the rate of change in the pixel data exceeds a selected threshold
that indicates a possible defect if it occurs in the data area of the
disk.
