According to an example, an apparatus for performing spectroscopy includes a perimeter wall extending between a first end and a second end of the perimeter wall along a first axis, in which an interior surface of the perimeter wall forms a hollow core extending along the first axis. The perimeter wall has openings at both the first end and the second end and light is to pass through the perimeter wall. The apparatus also includes a plurality of SES modules positioned around an inner circumference of the perimeter wall in a spaced arrangement with respect to each other to allow light to enter into the hollow core in gaps between the plurality of SES modules, in which each of the plurality of SES modules is positioned substantially across from a gap.