Browse Prior Art Database

Optical Profileometer for Surface Testing

IP.com Disclosure Number: IPCOM000083441D
Original Publication Date: 1975-May-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Whitefield, RJ: AUTHOR

Abstract

The apparatus illustrated measures the profile of a surface without physical contact. A laser beam is directed onto a surface at normal incidence and the diffracted or scattered light produced in reflection by the surface is processed by optics and electronics, as to yield a profile of the surface.

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Optical Profileometer for Surface Testing

The apparatus illustrated measures the profile of a surface without physical contact. A laser beam is directed onto a surface at normal incidence and the diffracted or scattered light produced in reflection by the surface is processed by optics and electronics, as to yield a profile of the surface.

As shown, laser beam 1, normally incident onto a surface 2 moving with a uniform velocity, returns both specular and diffracted components. The specular and diffracted components are collected and focused by lens L1 onto a light detector D1, yielding a reference signal SF representing the product of the laser intensity and the surface reflectance.

In the other optical path, lens L2 yields a Fourier transform of the reflected light at a plane containing a central obstruction 3, which removes the specular component. A subsequent lens, L3, in combination with a microscope objective L4 produces a magnified central dark field image of the surface 2. An aperture A1 located at the plane of this image restricts the field of view to a small area of the surface 2.

Subsequent lens L5 and L6 produce a scaled Fourier transform of the light beam passing through the aperture. This light beam is directed onto the surface of a continuous position sensing photodetector D2. The detector D2 yields two signals, a right signal SR and a left signal SL, representing the product of intensity in position of the right and left optical Fourier spectrum components about a central null axis.

The central null axis of the detector D2 is adjusted...