Optical activity

Optical activity is the rotation of a linearly polarized wave’s polarization direction as it travels through a medium, caused by different propagation speeds for left- and right-circularly polarized components.

Circular birefringence: A difference in refractive index or propagation speed between left- and right-circularly polarized waves. Its unequal phase accumulation turns their combined linear polarization.
Linear polarization: A polarization state in which an electromagnetic wave’s electric field oscillates along a fixed direction. Optical activity is defined by the changing direction of this state.
Polarimetry: The measurement of the rotation of polarized light by a sample. It quantifies optical activity using the angle of polarization rotation.
Linear birefringence: A difference in refractive index for two orthogonal linear polarization directions. It can alter polarization through a different anisotropy than circular birefringence.
Circular dichroism: The unequal absorption of left- and right-circularly polarized light by a material. Unlike optical activity, it changes component amplitudes rather than only their phase difference.
Circular polarization: A polarization state in which the electric-field vector rotates at constant magnitude as a wave propagates. Linear polarization can be decomposed into equal left- and right-circular components.
Saccharimetry: The measurement of sugar concentration through its effect on polarized light. Sugar solutions rotate polarization by amounts related to their concentration.
Optical rotation: The angular change in the plane of linear polarization caused by propagation through a medium. It names the measurable rotation produced by optical activity.
Jones calculus: A matrix formalism for calculating how optical elements transform fully polarized light. It represents polarization rotation as a transformation of the electric-field components.
Chirality: The property of an object or structure that makes it non-superimposable on its mirror image. Chiral structures often respond differently to the two circular polarizations.

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