Ultra low flying height measurements using monochromatic and phase demodulated laser interferometry

Phase demodulated laser interferometry and three wavelength monochromatic interferometry are employed to measure the flying height at the slider-disk interface in the sub-100 nanometer spacing range. Phase demodulated laser interferometry measures the relative displacement of the slider using the actual slider and disk, while three wavelength monochromatic interferometry measures the absolute flying height of the slider using a transparent disk and an actual slider. The results from both techniques are found to agree down to the "landing height", i.e., the height when the slider is "resting" on the top of the disk asperities. Landing heights are found to follow the peak-to-valley disk surface roughness.>