Optical inspection with alternating configurations

An imaging system for inspection of a sample, comprising:

• an illumination module, arranged to irradiate a surface of the sample with pulsed optical radiation;
• a mechanical scanner, arranged to translate at least one of the sample and a part of the imaging system to scan an area of the surface irradiated by the pulsed optical radiation and to irradiate a first frame and a plurality of successive, substantially overlapping frames on the surface by respective successive pulses of the pulsed radiation, each said successive frame having an overlap with a respective preceding frame of at least 50%;
• a collection module, arranged to collect the optical radiation scattered from the surface so as to capture a sequence of images of the first frame and the plurality of successive, substantially overlapping frames;
• a system controller, arranged to vary a configuration of the imaging system in alternation between at least a first configuration and a second, different, configuration, said alternation being synchronized with the pulsed optical radiation, whereby the sequence of images comprises at least a first set of images captured in the first optical configuration and a second set of images captured in the second optical configuration, and whereby at least two images of at least a portion of the area of the surface are captured, said at least two images comprising a first image captured using the first optical configuration and a second image captured using the second optical configuration;
• and
• an image processor, arranged to jointly process the first image and the second image to detect a defect in the sample by analyzing features on the surface as imaged using each of the first and the second optical configurations.