Horiba Scientific FluoroMax-4 Operation Manual page 163

® ®
FluoroMax -4 & FluoroMax -4P with USB rev. D (30 Jul 2012)
For single-photon excitation, the allowed values for the emission anisotropy are gov-
erned by:
r = 0.4 P
where P ( x )
2
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°
P
r
Values of 〈r〉 > 0.4 indicate scattered light is present in the measurement of 〈r〉. Values
of 〈r〉 < 0.2 indicate the rotation correlation time to be faster than the luminescence life-
time of the sample. 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 individual intensity components (I
raw polarization.
Experimentalists often multiply polarization units by 1000 to yield millipolarization
units, mP, for very small changes in the polarization.
Polarization geometries
Polarization measurements are taken in two basic geometries:
L-format uses two polarizers, which are both rotated between horizontal and verti-
cal 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
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
measurement 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
technique.
A schematic diagram of the L-format geometry is shown on the next page:
(cosα) (8)
2
2
3 x 1
is the second Legendre polynomial, and α is the angle between
2
–0.333
+0.5
–0.2
+0.4
, I , I , I ) are also referred to as
HH HV VH VV
®
-4 uses the L-format geometry.
10-3
Automated Polarizers