A defect inspection apparatus includes an illumination unit configured to irradiate a surface of a sample with a linear illumination spot; a condensing detection unit configured to condense reflected light of the illumination spot and to control a polarization state of the incident light to form an optical image; and a sensor unit configured to output the optical image and including an array-shaped light receiving portion and an antireflection film at a position conjugate with the illumination spot, in which the condensing detection unit includes a polarization control unit configured to increase light incident efficiency to the sensor unit. The normal line of the light receiving surface of the sensor unit is inclined from the optical axis of the condensing detection unit by 10 degrees or more and less than 80 degrees. The light condensing detection unit increases the optical magnification in the lateral direction of the illumination spot.

A measurement system is disclosed which includes a spot-traversal system for causing relative motion between a sample and an irradiation spot in a first direction, wherein the sample includes one or more fluorescent markers having respective fluorescence wavelengths, a gating system configured to provide a gating signal based at least in part on resultant light substantially at a wavelength of the irradiation spot, and an optical detection system configured to detect fluorescent light from at least some of the fluorescent markers irradiated by the irradiation spot, and provide detection signal(s) representing the fluorescent light detected concurrently with a gate-open condition of the gating signal.