Abstract: A system for detecting foreign particles or voids in the outer insulation jacket of an electrical cable is disclosed herein and utilizes a laser beam of electromagnetic radiation at a given wavelength, preferably within the far-infrared band. This laser is directed into the insulation jacket's cylindrical surface, which must be index-matched with a proper medium such that any portion thereof passing through the insulation jacket unobstructed by voids or foreign matter does so along a predictable primary beam path, and such that any portion impinging a void or foreign particle is caused to scatter along predictable scattering paths including paths which are different than the primary beam path. In this way, at least one detector can be properly aligned in at least one of these different scattering paths for detecting a portion of the scattered radiation, thereby indicating the presence of a void or foreign particle.