In 1809, French physicist François Arago discovered that polarized light undergoes rotation of its polarization plane when passing along the optic axis of quartz crystals.

Derivation of Optical Rotation Angle ($\alpha$)¶

The optical rotation angle $\alpha$ due to circular birefringence $\Delta n = n_L - n_R$ is:

$$\alpha = \frac{\pi d}{\lambda_0} (n_L - n_R)$$

Rotatory Dispersion¶

Arago and Jean-Baptiste Biot showed that rotation angle varies inversely with the square of wavelength: $\alpha(\lambda) \propto \frac{1}{\lambda^2}$.