Abstract: An apparatus including a source for producing a concentrated light beam, such as a laser, a background element spaced from the source against which the light beam is directed, and a transport arrangement for moving translucent bodies, such as French cut potatoes, through the light beam. When light from the source impinges upon a pure translucent body, the light is scattered or diffused within the body around the point of impingement so as to illuminate a surface area of the body larger than the cross-sectional area of the light beam, but light from the source impinging upon an impurity in the translucent body is scattered or diffused to a lesser extent. The background element is formed of a material which causes light from the source which impinges on it to be diffused within the material in a manner similar to the diffusion of the light in the translucent bodies.

Abstract: An apparatus including a source for producing a concentrated light beam, such as a laser, a background spaced from the source against which the light beam is directed, and a transport arrangement for moving translucent bodies, such as French cut potatoes, through the light beam. Another light source illuminates the background independently of the concentrated light beam. A receiver receives light reflected from the background and from translucent bodies moving through the light beam, as well as from the independent light source illuminating the background. The receiver produces an output signal which changes when an impurity enters the concentrated light beam, and this changed signal is used to operate a device which removes the impurity from the remainder of the translucent bodies. The light beam may be scanned across a plurality of rows of moving bodies by directing the beam at a rapidly rotating multifaceted mirror.