It also provides information about the secondary and tertiary structures of proteins.
Circular dichroism is the difference in the absorption of left and right circularly polarized light.
A periodic variation in the polarization of the light beam is induced by the polarization modulator through all ellipticities from left circular through elliptical, unchanged linear and elliptical to right circular. This polarized light passes through the sample to a photomultiplier detector. If the sample is not optically active, the light beam does not vary through this cycle. With the introduction of an optically active sample, a preferential absorption is seen during one of the polarization periods and the intensity of the transmitted light now varies during the modulation cycle. The variation is directly related to the circular dichroism of the sample at that wavelength.