-4 & FluoroMax
-4P with USB v. B (23 Oct 2009)
For single-photon excitation, the allowed values for the emission anisotropy are go-
〈r〉 = 0.4〈P
is the second Legendre polynomial, and α is the angle between
the molecule’s absorption and emission dipoles. The angle α may vary from 0 to 90°.
Thus the allowed values for 〈r〉 and P are:
Parameter α = 0° α = 90°
Values outside of this range indicate scattered light is present in the measurement of
〈r〉. If the sample is excited with depolarized light—a less common technique—the
measured value of P ranges from –1/7 to +1/3 (and 〈r〉 from –1/11 to +1/4). The indi-
vidual intensity components (I
) are also referred to as raw polarization.
Experimentalists often multiply polarization units by 1000 to yield millipolarization
units, mP, for very small changes in the polarization.
Polarization measurements are taken in two basic geometries:
• L-format uses two polarizers, which are both rotated between horizontal and vertic-
al positions for measurements. If the G factor is determined beforehand, only two
measurements are required: the VV and VH components, found by rotating only the
emission polarizer. The FluoroMax
-4 uses the L-format geometry.
• T-format uses one excitation and two emission polarizers. The excitation polarizer
is rotated between horizontal and vertical for measurements, while the emission po-
larizers are fixed—one horizontal and the other vertical. If the G factor is deter-
mined beforehand, it is possible to obtain the anisotropy or polarization in one mea-
surement cycle, for the VV and VH components are available simultaneously on the
two emission detectors. The G factor is measured differently in the T-format tech-
A schematic diagram of the L-format geometry is shown on the next page: