Fluorescence polarization

Fluorescence anisotropy is the phenomenon where the light emitted by a fluorophore has unequal intensities along different axes of polarization. Early pioneers in the field include Aleksander Jablonski, Gregorio Weber, and Andreas Albrecht. The principles of fluorescence polarization and some applications of the method are presented in Lakowicz's book.

The anisotropy (r) of a light source is defined as the ratio of the polarized component to the total intensity (${\displaystyle I_{T}}$):

${\displaystyle r={\frac {I_{z}-I_{y}}{I_{x}+I_{y}+I_{z}}}}$

When the excitation is polarized along the z-axis, emission from the fluorophore is symmetric around the z-axis(Figure). Hence statistically we have ${\displaystyle I_{x}=I_{y}}$. As ${\displaystyle I_{y}=I_{\perp }}$, and ${\displaystyle I_{z}=I_{\parallel }}$, we have

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