Determining the complex refractive index phase offset in interferometric

Abstract

An apparatus and method for optically measuring the air gap between a transparent glass disk and an air bearing slider without separately measuring the real index of refraction n and extinction coefficient k of the slider using an external ellipsometer. The phase offset required to compute the air gap is computed from a measurement of the air slider reflectivity and from an empirically derived equation that correlates the index of refraction with the reflectance of the slider. The apparatus includes a light source for directing a light beam through the transparent member and air gap, and onto the reflective slider. The light reflects off of the slider and the transparent member to create an interference pattern. The reflected light is detected by a photodetector that is coupled to a computer. The slider reflectivity r is found from the reflected light. An empirically derived linear equation which correlates the real part (n) of the slider refractive index to reflectivity (r) is next used to estimate n from r. Given n and r the phase offset and space can then be calculated.