Detection of subsurface defects by reflection interference
AssigneePolaroid Corporation
InventorWilliam J. Timson
Life of this patent
Estimating the term…
Abstract
A process for detecting defects in a multiply layered light transmitting structure, comprising illuminating the surface of the structure with a beam of light at an angle of incidence to the structure at which at least a portion of the beam will be reflected, and detecting the intensity of the reflected beam to locate subsurface as well as surface anomalies in the structure.
Claims14
The method of inspecting a layered material having at least one optically transmissive surface layer and at least one other layer adjacent said optically transmissive layer comprising the steps of moving said material past an inspection station, directing a beam of light onto said optically transmissive surface layer at an acute angle of incidence, focusing light reflected and scattered from said material onto intensity detecting means to produce a reflection interference signal determined by the relative phases and amplitudes of the reflected and scattered components of said beam, and detecting changes in said signal produced in the presence of anomalies in one or more of said layers.
The method of inspecting a multiply coated color negative comprising a plurality of photosensitive layers interspersed with dye layers comprising a set of dyes which together will absorb all light in the visible spectrum and transmit at least a portion of infrared light, said layers being coated on an opaque base sheet, comprising the steps of moving said negative past an inspection station, directing a beam of infrared light at the coated layers on said base sheet, focusing infrared light reflected and scattered from said layers onto a photodetector to produce a reflection interference signal determined by the relative phases and amplitudes of the reflected and scattered components of said beam, monitoring the position of said beam on said negative, and registering abrupt changes of said signal as a function of the position of said beam on said negative.
The method of inspecting a web comprising a plurality of layers on a base sheet, at least an outer set of said layers being at least partially transmissive to light of at least one wavelength, comprising the steps of moving said web past an inspection station, scanning said web with a flying spot of light at a wavelength at which said set of layers is at least partially transmissive, said flying spot being formed by a beam of light directed onto said layers at an acute angle of incidence, collecting light reflected and scattered from said layers, focusing said collected light on a photodetector to produce a reflectance interference signal determined by the relative phases and amplitudes of the reflected and scattered components of said beam, and detecting abrupt changes in said signal produced by anomalies in said layers.
Dependencies are inferred from the claim text.