Multiplexed laser interferometer for non-dispersed spectrum detection in a dynamic flying height tester

摘要

A preferred embodiment of the present invention comprises two laser sources of different frequency monochromatic light that are time-multiplexed through a beam combiner to produce composite beams that are steered to a gap between a slider and a disk. A reflected light that includes an interference pattern is then directed to an aperture plate that permits a spot of light to be directly detected by a photodiode which reads the intensity. Measurements of the intensity are taken at respective time-points to sample each laser source, and the measured intensities are compared to determine the slider to disk spacing. Since different frequency light will have different intensity for the same spacing, integer ambiguities can be directly resolved. In an alternative embodiment, several photodiode detectors are included with a multi-aperture plate that permits the simultaneous assessment of disk-to-slider spacing at several points of the slider dictated by the placement of multiple composite laser beams and the respective apertures.