Circular dichroism (CD) is the differential absorption of left- and right-handed circularly polarised light; a manifestation of optical activity.
Circular dichroism is exhibited naturally by chiral samples and can be induced moreover by certain influences such as a static magnetic field.
Today, circular dichroism is the most widely employed chiroptical technique.
One can distinguish between different types of CD depending on the frequency of the light.
An instrument designed to measure circular dichroism is known as a circular dichrograph or a circular dichroism spectrometer.
Most existing circular dichroism spectrometers make used of a photoelastic modulator (PEM) to rapidly modulate incident light between left- and right-handed polarisation states.
Snapshot circular dichroism (S-CD) is a novel approach towards measuring circular dichroism, introduced by Arteaga, El-Hachemi and Ossikovski in 2019 [Arteaga19a]. In S-CD, light with a spatially varying ellipticity is passed through a homogeneous sample and a snapshot is taken of the intensity of the emerging field. No PEM is used; spatial rather than temporal multiplexing. S-CD might open the door to faster measurements of CD than is possible using PEM and temporal modulation of input polarisation state.