Technique for measuring very small spacings

Boots – shoes – and leggings

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364561, 356357, 360 75, G01B 1114

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045933685

ABSTRACT:
The spacing between two surfaces such as the space between a glass disk and a magnetic head or slider is measured by directing light from a broad spectrum light source onto the two surfaces, and combining the reflected light, with the light at different frequencies being combined constructively and destructively. The combined signals are analyzed at a large number of wavelengths to give a plot of intensity vs. wavelength, and the wavelength or wavelengths of maximum intensity (and constructive interference) and/or minimum intensity (destructive interference) are identified. For a glass disk and a metal slider with normal incidence, the light intensity minima occur at d=(1/2)nL and maxima at d=(1/2) (n-1/2) L, where d is the separation, L is the wavelength and n is a positive integer indicating the order. The actual plot of intensity vs. wavelength is correlated with the theoretical intensity vs. wavelength function, and this correlation or curve fitting is carried forward to calculate the spacing "d" to any desired accuracy within the limits of the input data. The entire process for determining the spacing takes only a few seconds. In accordance with one useful relationship for example, the spacing "d" is shown to be equal to ##EQU1## where L.sub.1 and L.sub.2 are successive wavelengths where the intensity is a maximum and a minimum, or vice versa. Other examples of curve fitting or correlation, both simpler and more complex are developed. After the spacing "d" has been determined, the spacing may then be increased or decreased toward a desired value and the method repeated.

REFERENCES:
patent: 3601492 (1971-08-01), Reichard
patent: 3751643 (1973-08-01), Dill et al.
Bowen et al., "Interferometer Alignment Tool", IBM Technical Disclosure Bulletin, vol. 15, No. 12, pp. 3691-3692, May, 1973.
Heinrich, "Semi-Automatic Flight Height Measuring for Magnetic Heads", IBM Technical Disclosure Bulletin, vol. 20, No. 4, p. 1503, Sep. 1977.
Makosch et al., "Measuring the Flight Height of Magnetic Heads on Magnetic Disks", IBM Technical Disclosure Bulletin, vol. 15, No. 4, pp. 1322-1323, Sep. 1972.

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