Polarized Light, Linear Dichroism, and Circular Dichroism

Abstract

Synonyms Anisotropic spectroscopy; Spectroscopy of chiral molecules; Spectroscopy of oriented systems

Definition Spectroscopic techniques that use polarized light can provide more information about the samples being studied than those that use unpolarized light. Two techniques of particular utility for biomolecular samples are linear and circular dichroism. Linear dichroism (LD) is the difference in absorption, A, of light linearly polarized parallel (//) and perpendicular (⊥) to an orientation axis (Nordén et al. 2010; Rodger and Nordén 1997; Michl and Thulstrup 1986):

LD = A// – A⊥

LD is used with systems that are either intrinsically oriented or are oriented during the experiment.

Circular dichroism (CD) is similarly the difference in absorption of left and right circularly polarized light (Cantor and Schimmel 1980; Craig and Thirunamachandran 1984; Michl and Thulstrup 1986; Rodger and Nordén 1997; Berova et al. 2000; Barron 2004; Nordén et al.... Show more