Non-ambiguous measurement of disk/slider spacing and effective optical constants with circular heterodyne interferometry

A method for non-ambiguous measurement of disk/slider spacing was reported here. By employing the circular heterodyne interferometric technique and the multiple-beam reflection theory at specific oblique incident angle, both the disk/slider spacing and the effective optical constants could be determined with a single optical configuration. With this method, the extreme values of the phase difference or the intensity variation by moving the slider in forward/backward motion were no longer required. The theoretical derivation revealed that the optimal resolution attainable on the measurement of the flying height was better than 0.025 nm. Owing to its common-path configuration, this method was also free from environmental vibrations. Hence, high stability and accuracy could be achieved relatively with ease based on the simple optical configuration and straightforward measurement procedures.