Consideration and compensation for precision optical flying height measurement

Abstract

It is a big challenge to determine ultra-low slider flying height accurately. The intensity interferometry flying height testing method is widely used to determine slider flying height. However, the intrinsic measurement errors of the method are becoming non-negligible with the decrease in slider flying height. Strategies have to be developed to minimize the errors. To measure flying height with a normal incidence optical flying height tester, a calibration process is required to determine several constants used in flying height calculation. In practice, the calibration is usually done simply by retracting the slider from the disk and measuring the intensity minima and maxima of the interferogram during the retracting process. It has been demonstrated that the single most important source of error in the flying height measurement is associated with errors in the determination of the intensity maxima and minima. In this work, the effects of optical filter, the responding frequency of photodetector, and the lack of the first order intensity minimum on the determination of the intensity maxima and minima are studied. Methodologies to minimize the errors in flying height measurement caused by the above factors are developed.

A double common-path heterodyne interferometer for the measurement of flying height modulation

“…Consequently, instruments are required to study in detail the dynamic properties or the FHM of the flying slider. In this paper, we propose a novel FHM measurement method using a double common-path heterodyne interferometer with a transverse Zeeman laser [18,19], which has the advantages of high resolution, quick frequency response and direct traceability to the international standard (IS) so as to be exempt from the calibration which is required in intensity interferometry [20]. The resolution reaches 0.1 nm in terms of phase measurement [21], and the frequency of data sampling can be higher than 500 kHz.…”