  The chirality of an object can be studied by measuring the circular
dichroism, that is, the difference in absorption of light with different
helicity. The chiral optical response of an object, however, can have two
different origins. On the one hand, it can be linked to the chiral geometry of
the object. On the other hand, it can be linked to the chiral material from
which the object is made. Whereas previously, no distinction between the two
contributions could be made, we report here a computational approach that
allows us to separate these two contributions to the circular dichroism of an
object. We consider separately the cases where geometry-related resonances
affect the optical response and where they are absent. In both cases, we find
the circular dichroism to be easily decomposable if a geometrically achiral
object has a similar absorption spectrum to the chiral object under
investigation. Furthermore, in the non-resonant case, the contribution
attributed to the material can be obtained without taking any geometry into
account. Besides being of fundamental importance, the possibility of
disentangling both contributions will be important for guiding the future
design of chiral objects and devices.
