Patent ID: 8283622

Claim:
Apparatus for testing a magnetic medium, comprising: a magnetic field generation sub-system configured to apply a magnetic field of a time-varying strength to a portion of the magnetic medium; a light generation sub-system configured to direct a polarized optical beam towards the portion of the magnetic medium that is in the magnetic field, wherein the optical beam is reflected by a surface of the magnetic medium at a point of incidence in the magnetic field; a motion sub-system configured to move the magnetic medium relative to the optical beam so as to cause the point of incidence to repeatedly traverse each of a plurality of sectors along a track on the surface of the magnetic medium, wherein the magnetic field generation sub-system and the motion sub-system cooperate to vary the strength of the magnetic field in synchronization with motion of the point of incidence along the track; a measurement sub-system configured to obtain a series of Kerr signal measurements of the reflected optical beam as the point of incidence repeatedly traverses the sectors, each Kerr signal measurement being associated with (1) a corresponding one of the sectors in which the point of incidence was when the Kerr signal measurement was obtained and (2) a corresponding strength of the magnetic field at the time when the Kerr signal measurement was obtained; and a control sub-system configured to group the series of Kerr signal measurements into ensembles such that the Kerr signal measurements in an individual ensemble are all associated with the same one of the sectors, the control sub-system being further configured to determine at least one magnetic property of at least one of the sectors from the Kerr signal measurements in the corresponding ensemble.