During field operation of a heat-assisted magnetic recording data storage device, a laser adjustment procedure is performed. The laser adjustment procedure involves writing on a recording medium at least three tracks. If a bit error rate of a middle tracks has increased, the laser current is swept while recording test tracks to determine a new laser current that results in a minimum bit error rate. The new laser current is used for subsequent write operations.

An apparatus comprises a spindle to rotate a magnetic recording medium and a magnetic field generator to expose a track of the medium to a DC magnetic field. The magnetic field generator is configured to saturate the track during an erase mode and reverse the DC magnetic field impinging the track during a writing mode. A laser arrangement heats the track during the erase mode and, during the writing mode, heats the track while the track is exposed to the reversed DC magnetic field so as to write a magnetic pattern thereon. A reader reads the magnetic pattern and generates a read signal. A processor is coupled to the reader and configured to measure one or more magnetic properties of the track using the read signal. The apparatus can further comprise a Kerr sensor that generates a Kerr signal using the magnetic pattern.

The disclosure disclose a light source unit applied to the thermally assisted magnetic head. A welding layer and a stopping structure are disposed between the slider of the thermally assisted magnetic head and the light source unit. When the light source unit is joined with the slider, the light source unit moves as the welding layer melts and can be precisely limited at the preset position by the stopping structure. In this way, the emission opening of the light source unit and the waveguide can be aligned precisely, thereby increasing the optical coupling efficiency between the light source unit and the waveguide. Meanwhile, the embodiment of the disclosure further accordingly provides a thermally assisted magnetic head, a head gimbal assembly, and a hard disk drive.

The disclosure disclose a light source unit applied to the thermally assisted magnetic head. A welding layer and a stopping structure are disposed between the slider of the thermally assisted magnetic head and the light source unit. When the light source unit is joined with the slider, the light source unit moves as the welding layer melts and can be precisely limited at the preset position by the stopping structure. In this way, the emission opening of the light source unit and the waveguide can be aligned precisely, thereby increasing the optical coupling efficiency between the light source unit and the waveguide. Meanwhile, the embodiment of the disclosure further accordingly provides a thermally assisted magnetic head, a head gimbal assembly, and a hard disk drive.