A double-sided optical inspection system is presented which may detect and classify particles, pits and scratches on thin film disks or wafers in a single scan of the surface. In one embodiment, the invention uses a pair of orthogonally oriented laser beams, one in the radial and one in the circumferential direction on both surfaces of the wafer or thin film disk. The scattered light from radial and circumferential beams is separated via their polarization or by the use of a dichroic mirror together with two different laser wavelengths.