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Microscope Interferometer

IP.com Disclosure Number: IPCOM000079533D
Original Publication Date: 1973-Jul-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Edwards, RB: AUTHOR

Abstract

This interferometer is used to measure tape-to-head air film thickness, by simultaneously illuminating this interface with both pulsed laser energy and pulsed white light energy. The laser's reflected interference fringe pattern produces a Fizeau pattern containing information as to the variable thickness air film at this interface. The white light reflected interference pattern produces a fringes of equal chromatic order (FECO) pattern, providing an absolute distance reference. In combination, these two patterns provide accurate measurement of this air film thickness.

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Microscope Interferometer

This interferometer is used to measure tape-to-head air film thickness, by simultaneously illuminating this interface with both pulsed laser energy and pulsed white light energy. The laser's reflected interference fringe pattern produces a Fizeau pattern containing information as to the variable thickness air film at this interface. The white light reflected interference pattern produces a fringes of equal chromatic order (FECO) pattern, providing an absolute distance reference. In combination, these two patterns provide accurate measurement of this air film thickness.

Improved Fizeau fringe sharpness is achieved due to the excellent spatial and temporal coherence of the laser source. Short duration pulses permit the operator to "freeze" the dynamic air film conditions. This figure is not to scale, and is intentionally presented out of scale to enhance an understanding of this interferometer.

Aluminized tape 10 is moved past stationary magnetic recording head 11, or a model thereof, at a controlled speed, which may include a start-stop sequence. While the tape is moving, a hydrodynamic air film 12 is established between the tape and the head. The thickness of this air film is in the range of a few microinches and is affected by parameters such as head contour, tape speed and tape tension.

A pulsed laser 13, operating at a single monochromatic visible wavelength, and with an extremely short pulse duration of about 500 nanoseconds, has its...