Atlantic Research Corporation

Sandor Holly

Shui Lin Chao

Method and apparatus for sensing the effective magnitude and/or number and/or position of individual depression and/or protrusion defects on a high-precision smooth surface of an article which may have said defects randomly distributed and relatively spatially distant each from the other, comprising continuously scanning the surface with a laterally-moving interference fringe pattern adjusted in size to have a cross-sectional area substantially smaller than the surface and no larger than an area which includes about an average predetermined spatial incidence of about one defect per pattern area; adjusting the fringe period to a size substantially larger than the effective cross-sectional dimension of a predetermined, maximum size defect; continuously sensing the AC and DC or AC signal components of the backscattered light; and substantially determining the effective magnitude and/or number and/or surface position of said defects by determining the magnitude of the AC or AC and DC signals obtained at each instantaneous relative position of the fringe pattern and the smooth surface. Said scan can thus provide information as to effective magnitude, number of defects, and topography of the defects on the surface. By the use of appropriate electronics, the information can be recorded and/or displayed.

Process and apparatus for sensing defects on a smooth surface

Method and apparatus for determining the width of an elongated element, such as a filament or slit which comprise producing a moving interference fringe zone by converging two beams of coherent light of the same intensity but slightly different frequency; positioning the element within the fringe zone in such manner that the longitudinal axis of the element is substantially normal to the plane of the convergent beams, namely, parallel to the plane of the fringes; maintaining the element substantially spatially stationary relative to the zone, whereby the moving fringe pattern continuously sweeps across the element; and determining the ratio of the AC to DC signal components of the radiation scattered or transmitted by the element. The method and system include respectively the step and means therefor of adjusting or scanning the fringe period value around the element to determine the size capable of producing a minimum AC/DC ratio. In the case of a system substantially free from noise, including non-compensating optical noise factors introduced by the element being measured, a zero ratio indicates that the filament diameter or slit width equals the known fringe period, and a non-zero ratio indicates diameter or slit width deviation from the fringe period, the degree of which can be determined from the signal ratio with the use of known means by adjusting the fringe period until the AC component of the signal becomes zero. In the case of a system having a substantial amount of noise, the AC/DC minimum ratio obtained at a given fringe period may have a finite value and indicates an element width equal to the given fringe period times a constant, the constant being the ratio of the width of the given element and the given fringe period. The element, though spatially stationary in the fringe zone, can be continuously moving longitudinally. The process and system are particularly useful for monitoring the width of manufactured elements and, by automatic feedback, correcting deviations. In some applications where change in the magnitude of the DC signal component during the fringe period scan is sufficiently nominal with respect to permissible width-sensing error, the AC/DC ratio measurement can be dispensed with and determination of the AC signal component minimum alone can be employed.

Process and apparatus for filament or slit size monitoring

Device and process for testing the optical transfer function of a lens system which comprise employing as the object or target the laterally moving-fringe pattern produced by convergence of two monochromatic coherent-radiation beams of equal size and intensity and slightly different frequency. A second fringe pattern may be employed as the reference standard. Both the target and reference patterns can be varied simultaneously in spatial frequency or fringe period. The system and process can test both modulation transfer function and phase transfer function accurately at any monochromatic wavelength produced by an available coherent-radiation source to which the test lens system is transparent, e.g., ultraviolet or shorter, visible, and infrared or longer. When polarized monochromatic radiation is used, the invention can also be employed to determine the polarization characteristics of the lens. The system and process can also test chromatic aberration by successive use of different coherent monochromatic radiation wavelengths.

Device and process for testing a lens system

Process and apparatus for sensing the angular orientation of a line or slit element, which comprise producing a laterally moving interference fringe zone wherein the fringe period is substantially wider than the element or the positive difference between the width of the element and a integer multiple of the fringe period, by converging two beams of coherent light of equal intensity and different frequency; positioning the portion of the article bearing the element within the fringe zone such that the article lies in a plane defined by the x and y axes in the fringe pattern and the element is in a position, relative to the article, such that its longitudinal axis is substantially parallel to the fringe plane or can, by rotation of the fringe zone relative to the article around the z-axis, be brought into fringe-plane parallel position; rotating the fringe zone and/or the article around the z-axis to produce relative angular rotation between them; and determining the ratio of AC to DC signal components of the radiation scattered by the line or transmitted by the slit as rotation around the z-axis continues. The maximum AC/DC ratio indicates parallel fringe-plane alignment of the element and the degree of angular rotation from a given relative position of the fringe plane and the element to a succeeding position of parallel fringe-plane and element alignment indicates the angular orientation of the element on the article.

Process and apparatus for monitoring angular orientation

Process and apparatus therefor for sensing the magnitude and direction of lateral displacement of at least one line or slit element of an article which comprises producing two coherent light beams of the same intensity, one of the beams having a different frequency from that of the other beam, the frequency difference .DELTA.f being within the radio frequency range; converging the two beams to form an interference zone comprising, within the zone of convergence, a fringe pattern characterized by continuous lateral movement at a rate equal to .DELTA.f; adjusting the fringe period of the pattern to a width which is substantially wider than the element or the positive difference between the width of the element and an integer multiple of the fringe period; positioning at least the portion of the article bearing the element within the interference zone in such manner that the article lies in a plane defined by the x and y axes of the fringe pattern and the element is in a position, relative to the article, such that its longitudinal axis is substantially parallel to a fringe plane; laterally shifting the fringe zone and/or the article along the y-axis to produce relative lateral displacement between them while maintaining the element in substantially parallel fringe-plane alignment at least within the central portion of the fringe zone; continuously determining the phase of the RF signal component of the radiation scattered or transmitted by the element as the relative lateral displacement between the zone and article continues from a first to a second position of the element within the fringe zone; simultaneously and continuously comparing the phase of the scattered or transmitted radiation RF signal with the phase of a constant reference RF of .DELTA.f frequency; and sensing the magnitude and direction of phase shift between the RF signal component of the scattered or transmitted radiation and the RF reference between the first and second positions, whereby the magnitude indicates the extent of lateral displacement of the element between the two positions and the direction indicates the direction of relative lateral displacement. The element can comprise a single element, two essentially parallel elements, or a plurality of elements wherein at least each two adjacent elements are substantially parallel. The process and apparatus are particularly useful for accurate measurement of fractional distances between two elements with a high degree of fine resolution; the total magnitude and direction of displacement of elements of a measuring device, such as an encoder; and the distance from a reference element to a desired position on the article.

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Falls Church, VA, United States of America

Sandor Holly