Improved intensity interferometry method for measuring head-disk spacing down to contact

In this paper, we give a detailed analysis of the working principle, application limits, and potential problems of the intensity interferometry flying height testing, one of the most popularly-used flying height testing techniques. Then, phase-shift methods are proposed to improve the sensitivity of this technique when the head-disk spacing is below 10 nm or near contact. This is based on fabricating the glass testing disk to have a specified thickness, or having it coated with a specified thickness thin carbon film. Theoretical analysis, numerical evaluation, and experimental considerations are presented.