A method comprises storing a first laser current value in response to a photodetector sensing that a threshold current for a laser diode of a HAMR head has been reached, the photodetector situated proximate the laser diode. The method also comprises storing a second laser current value in response to a sensor sensing that the threshold current for the laser diode has been reached, the sensor situated away from the laser diode. The method further comprises determining a difference (delta) between the first and second laser current values, repeating the storing and determining processes during subsequent use of the laser diode, and detecting a change in the delta indicative of a malfunction of the head.

A method comprises writing a waveform on a magnetic recording medium using a heat-assisted magnetic recording apparatus which includes a laser. The method also comprises reading back the waveform from the medium, and detecting one or more transition shifts in the readback waveform indicative of a mode hop of the laser. The method further comprises measuring a metric of the one or more transition shifts.

A test involves iterations over a series of laser powers of a heat-assisted read/write head. The iterations involve writing to a recording medium at the selected laser power for a sufficient duration to ensure thermal equilibrium of the read/write head at an end of the write. A clearance-control heater of the read/write head is transitioned from a pre-write power before a start of the write to a steady-state write power. The iterations further involve measuring a temperature of the read/write head during the write and adjusting the steady-state write power to achieve a predefined difference between the temperature at the start of the write and the end of the write. The adjusted steady state write power is stored for each iteration. A write-induced protrusion is determined based on the iterations and used for calibration of the read/write head.

A method of writing data to a transparent substrate comprises forming a first voxel by focusing a first laser pulse on a first location in a transparent substrate; and forming a second voxel by focusing a second laser pulse on a second location in the transparent substrate. The first laser pulse and the second laser pulse have different amplitudes, resulting in the first and second voxels having different strengths. Also provided are a system useful for implementing the method; an optical data storage medium obtainable by the method; and a method of reading data from the optical data storage medium.

A method of writing data to a transparent substrate comprises forming a first voxel by focusing a first laser pulse on a first location in a transparent substrate; and forming a second voxel by focusing a second laser pulse on a second location in the transparent substrate. The first laser pulse and the second laser pulse have different amplitudes, resulting in the first and second voxels having different strengths. Also provided are a system useful for implementing the method; an optical data storage medium obtainable by the method; and a method of reading data from the optical data storage medium.

Various illustrative aspects are directed to a data storage device comprising one or more disks; one or more heads, including a first head having a first laser diode and a near field transducer; and one or more processing devices configured to: preheat the first LD to a steady state temperature; write a first and a second series of writings at a plurality of thermal fly-height control powers, wherein the first and the second series of writings are written at the steady state temperature, and the first series of writings are of a shorter duration than the second series of writings; determine, for the first head, an NFT protrusion measurement based at least on a difference in TFC power used between (1) one of the first of writings and (2) one of the second series of writings, at a corresponding written signal amplitude.

Provided are arrangements of optical elements that combine the features of a high power, compact laser that exhibits narrow linewidth output and that does not appreciably shift in wavelength or vary in power over a wide range of temperatures. Such arrangements include a transmission filter and a Bragg reflector that select out the wavelength for which the output power of a reflective semiconductor optical amplifier (RSOA) is least affected by changes in temperature over a temperature range of interest. Such arrangements may also utilize temperature-insensitive materials.

Mode hop detection is provided. A device includes circuitry to receive, from a reader element an indication of one or more properties of a magnetic medium detected by the reader element. The device includes circuitry to determine an envelope of the signal. The device includes circuitry to adjust, responsive to the envelope, a current provided to a laser configured to heat the magnetic medium.

Mode hop detection is provided. A device includes circuitry to receive, from a reader element an indication of one or more properties of a magnetic medium detected by the reader element. The device includes circuitry to determine an envelope of the signal. The device includes circuitry to adjust, responsive to the envelope, a current provided to a laser configured to heat the magnetic medium.

Mode hop detection is provided. A device includes circuitry to receive, from a reader element an indication of one or more properties of a magnetic medium detected by the reader element. The device includes circuitry to determine an envelope of the signal. The device includes circuitry to adjust, responsive to the envelope, a current provided to a laser configured to heat the magnetic medium.