Patent ID: 7307714

Claim:
A process for detecting internal inclusions in a solid internally transmissive substrate, the process comprising the following steps: (i) providing the substrate, the substrate having a first major surface, a second major surface opposite the first major surface, and at least one side surface, wherein at least one of the first major surface, second major surface, and the at least one side surface optionally comprise light scattering defects that prevent direct inspection of the solid substrate in a gas medium; (ii) applying a light-absorbing non-transmissive black coating on the second major surface; (iii) placing the substrate having the black coating on the second major surface into an index-matching fluid having a refractive index matching that of the substrate; (iv) providing a collimated light beam; (v) scanning at least part of the substrate by passing the collimated light beam through the index-matching fluid and the side surface and through the substrate; (vi) detecting, at a position on the side of the first major surface, light scattered by an internal inclusion, when the collimated light beam is intercepted by the internal inclusion; and (vii) determining and storing the presence of the internal inclusion and at least one of location and size of the internal inclusion in the scanned part of the substrate.