Abstract: Disclosed are process and apparatus for inspecting internal inclusions in internally transmissive substrates. The process involves applying a black coating to one major surface of the substrate, submerging the substrate in a refractive index-matching fluid, and scanning the substrate with a collimated light beam. The scattered light signals produced by the inclusions can be detected by the human eye or by using a light detector. By the use of index-matching fluid and the black coating, the signal-to-noise ratio of the process and apparatus are enhanced. A preferred black coating is one cured from an electron beam or photo polymerizable coating composition applied to the major surface. The process and apparatus are particularly suitable for inspecting internal inclusions in an internally transmissive substrate having considerable amount of surface defects or contoured surface that prevent it from inspection in a gas medium.

Abstract: A process for detecting inhomogeneities, specifically, striae in a sample of fused silica glass is provided which includes the steps of: preparing a digitized phase plot for the sample using an interferometer which produces a beam of light which passes through the sample; applying a high pass filter to the phase plot to remove the effects of the sample's bulk properties; applying a statistical filter to the high pass filtered data to remove outlying data points; and column averaging the statistically filtered data. If present, striae can be readily detected in the column averaged, statistically filtered data.

Abstract: A device for quickly and accurately comparing the refractive index of an optical immersion liquid with the refractive index of a reference glass that the liquid is to be used with. The device comprises a cavity to at least partially contain the immersion liquid by the reference glass. The containment may be total, as in a hollow core, or may be between two windows composed of the reference glass and assembled in a spaced, facing relationship, one window having an inner face with a plano portion and a portion with a continuous slope, and a cavity intermediate the windows to contain the liquid being compared. The cavity is then filled with the liquid to be compared, transmitting laser light through the windows and the liquid to form an optical interference pattern.