Performance monitoring of a near-field transducer of a heat-assisted magnetic recording slider

An apparatus, comprising:

• a laser diode configured to generate light during a write operation;
• a slider comprising a near-field transducer (NFT) and an optical waveguide, the slider configured for heat-assisted magnetic recording and to communicate the light to the NFT via the waveguide;
• a writer heater of the slider configured to receive power during the write operation;
• a thermal sensor situated on the slider so as to be substantially insensitive to heat conducted from the NFT to the sensor, the thermal sensor configured to produce a sensor signal in response to sensing back-heating from a magnetic recording medium while the slider is spaced apart from the medium and the NFT generates heat during a write operation;
• and
• circuitry coupled to the thermal sensor, the circuitry configured to measure back-heating from the medium using the sensor signal and generate an output signal indicative of NFT performance degradation in response to the back-heating measurements.