A data storage device is disclosed comprising a disk and a head actuated over the disk, wherein the head comprises a laser configured to heat the disk while writing data to the disk. The laser power is adjusted and a pattern is written to a target track at the adjusted laser power. The pattern is read from the target track to generate a read signal, and a quality metric is generated based on the read signal. The process is repeated at least once, and a write power for the laser is configured based on a slope of the quality metric.