HAMR Writing Process Model-Based Compensation of Laser-Induced Transients

An established model is presented, which includes relative slow write head protrusion, fast near-field transducer (NFT) only protrusion, and heat transient process for heat-assisted magnetic recording writing process. Based on this model, equations are derived to calculate the write head and NFT only protrusions as a function of writing duty cycle. Then, we demonstrate how to compensate for the protrusion-caused NFT-to-media spacing change by thermal fly-height control for three different writing conditions of duty cycle from low to high, namely, repeatable run-out field write, servo pattern write, and user data field write. Finally, we present how to compensate for the impacts caused by fast transient processes, which include NFT only protrusion and heat transient process, within each servo wedge or data sector. There are two methods presented, pole placement method and deconvolution method. Both the methods produce very similar input laser profiles, which will cause approximately step change at the output signal magnitude responses from the simulation.