apparatus for detecting and mapping defects in the surfaces of polycrystalline material in a manner that distinguishes dislocation pits from grain boundaries includes a first laser of a first wavelength for illuminating a wide spot on the surface of the material , a second laser of a second relatively shorter wavelength for illuminating a relatively narrower spot on the surface of the material , a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through , and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light . a center blocking aperture or filter can be used to screen out specular reflected light , which would be reflected by nondefect portions of the polycrystalline material surface . an x - y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate raster mapping , recording , and displaying of respective dislocation and grain boundary defect densities . a special etch procedure is included , which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities . a reflectance measurement of the piece of material is obtained by adding together the signals from the optical detection devices . in the case where the piece of material includes a photovoltaic device , the current induced in the device by the illuminating light can be measured with a current sensing amplifier after the light integrating sphere is moved away from the device .