A light engine for detecting a defect is provided. The light engine comprises a waveguide. The waveguide comprises a first surface that is partially transmissive-reflective, and a second surface opposite to the first surface. The waveguide is configured to receive, on an input port, an input wavefront and provide waveguiding of the input wavefront by internal reflection between the first and second surfaces thereby replicating the input wavefront along a replication direction. The light engine further comprises a light detector positioned to measure an intensity of a residual portion of the holographic wavefront after waveguiding is provided by the waveguide.