Abstract: 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.