Circular dichroism spectroscopy measures the absorption of circularly polarized light. Circular dichroism and circular birefringence are manifestations of optical activity. Circular birefringence and circular dichroism are the manifestations of optical activity. Calculations also indicate birefringence and dichroism at high fields. Extrinsic 3d chirality causes large optical activity and linear conversion dichroism in metamaterials. Strong circular conversion dichroism due to extrinsic 2d chirality has been observed in metamaterials. In these compounds the readout is by circular dichroism rather than by ordinary spectroscopy. Conformational changes can be measured using circular dichroism or dual polarisation interferometry. It is the extension of circular dichroism spectroscopy into the infrared and near infrared ranges. Circular dichroism spectrometers contain a monochromator, for example. Circular conversion dichroism with almost ideal efficiency has been achieved in metamaterial-based chiral mirrors. Circular dichroism (CD) is the differential absorption of left- and right-handed circularly polarized light. This unequal absorption is known as circular dichroism. Molar ellipticity is circular dichroism corrected for concentration. Optical rotary dispersion and circular dichroism share the same quantum information content.