A sensor module is disclosed for a metrology apparatus. The sensor module comprises an illumination device for illuminating a structure on a substrate, said illumination device comprising at least a first set of illuminators and a second set of illuminators, wherein said first set of illuminators comprise one or more illuminators which are each operable to illuminate said structure with first illumination comprising a first optical characteristic and wherein said second set of illuminators comprise one or more illuminators which are each operable to illuminate said structure with second illumination comprising a second optical characteristic different to said first optical characteristic; an optical system being operable to capture scattered radiation scattered by the structure resultant from the structure being illuminated; and a detector operable to detect the scattered radiation.

An optical measurement system capable of suppressing noise and realizing more accurate measurement is provided. The optical measurement system includes a light source, an image sensor, and an optical system including a beam splitter that divides light from the light source into first light and second light. The optical system can configure a first optical system that records with the image sensor, a first hologram resulting from modulation of first light with second light while there is no sample, the second light being diverging light, and a second optical system that records with the image sensor, a second hologram resulting from modulation with second light, of light obtained by illumination of a sample with first light. The second optical system includes a restriction mechanism that restricts spread of the light obtained by illumination of the sample with first light to be kept within a predetermined range.

A hologram acquisition apparatus and a hologram acquisition system are disclosed. A hologram acquisition apparatus includes a beam splitter configured to split light emitted from an object into a first beam and a second beam, a first reflective optical element configured to receive and emit the first beam to the beam splitter, and a second reflective optical element configured to receive and emit the second beam to the beam splitter and formed as an annular spherical array having discontinuous surfaces, wherein the second reflective optical element has a plurality of segment regions that are concentric and divided to have the discontinuous surfaces and, the plurality of segment regions are formed to have the same focal point.