Effective refractive index method for frustrated total reflection: application to measurement of flying height

In order to measure the spacing between an actual magnetic disk and a slider, we developed a flying height sensor based on frustrated total reflection (FTR). When optically measuring the flying height of a slider, the phase shift on reflection at the magnetic disk is a significant problem. In this paper, we describe the theoretical treatment of the problem, introduce the modified effective refractive index method, and measure the effective refractive index of an actual magnetic disk. The flying height on a magnetic disk was also measured using the obtained effective refractive index. The result was compared with flying height measurements measured by the traditional interference method. They agreed with each other, with an error of less than 2.5 nm.