Abstract: A method and system for monitoring in real-time changes in operating conditions such as temperature of a magnetic super resolution magneto-optical system which produce variations in aperture size in the media readout layer. The magnitude of a magneto-optical (MO) amplitude signal in a reflected laser beam is monitored, normalized by dividing by the laser power, compared to the amplitudes in a table of stored values, and used to derive a laser power feedback signal for controlling the power of the laser to maintain a predetermined aperture size. The MO amplitude signal is derived from patterns representing calibration tones prerecorded onto portions of the data tracks of the MSR media.