# Time-resolved anisotropy

Time-resolved anisotropies measure the depolarization of fluorescence light. Parallel polarized light is used to excite the sample. The fluorescence of this samples is the detected polarization resolved by a vertical and parallel detection channel. A normalized difference of the time-resolved fluorescence intensities of these detection channels measures the depolarization of the sample independently of absolute fluorescence intensities.

The time-resolved anisotropy, r(t), is obtained by fluorescence intensity of the sample excited by parallel polarized light.  A normalized difference of the fluorescence light detected by a parallel, VV, and perpendicular, VH, detector defines the time-resolved anisotropy.
$$r(t) = \frac{f_{VV}(t) – f_{VH}(t)}{f_{VV}(t)+2\cdot G \cdot f_{VH}(t)}$$
Here G is the G-factor of the instrument, which corrects for the detection efficiency for the parallel and perpendicular light.
$$f_{VV}(t) = \frac{1}{3} f(t) \cdot \left(1 + 2 \cdot r(t)\right)$$
$$f_{VH}(t) = \frac{1}{3} f(t) \cdot \left(1 – r(t)\right)$$