An apparatus for detecting defects on a sample is provided. The apparatus includes a stage for receiving a sample to be inspected, and a first light source configured to generate an incident light beam to illuminate the sample on the stage. The first light source is configured to sequentially emit light of different wavelengths in wavelength sweeps. The apparatus also includes imaging optics for collecting light scattered from the sample and for forming a detection light beam, a detector for receiving the detection light beam and acquiring images of the sample, collection optics disposed within the detection light beam and configured to direct the detection light beam to the detector, and a first light modulator. The first light modulator is configured to filter out signals from the detection light beam, where the signals originate from uniform periodicity of uniformly repeating structures on the sample.