Ultra low head–disk spacing measurement using dual beam polarisation interferometry

In this paper, a dual-beam normal incidence polarisation interferometer is proposed to measure the flying height or head–disk spacing. Using this interferometer, the head–disk spacing can be measured both in magnetic real disk condition and in glass disk condition. It has the advantage of both the currently popular intensity interferometry method and the oblique incidence polarisation interferometry method. With this polarisation interferometer, not only the flying height can be measured down to contact without losing accuracy, but the pitch and roll of the head-slider can also be detected dynamically. The optical parameters of the head-slider can also be determined. Design details and experimental study are presented.