Emission linearly polarized

Let us consider tire case of a donor-acceptor pair where tire acceptor, after capturing excitation from tire donor, can emit a photon of fluorescence. If tire excitation light is linearly polarized, tire acceptor emission generally has a different polarization. Common quantitative expressions of tliis effect are tire anisotropy of fluorescence, r, or tire degree of polarization,... 

Steady-State Fluorescence Depolarization Spectroscopy. For steady state depolarization measurements, the sample is excited with linearly polarized lig t of constant intensity. Observed values of P depend on the angle between the absorption and emission dipole moment vectors. In equation 2 (9), Po is the limiting value of polarization for a dilute solution of fluorophores randomly oriented in a rigid medium that permits no rotation and no energy transfer to other fluorophores ... 

The fluorescence depolarization technique excites a fluorescent dye by linearly polarized light and measures the polarization anisotropy of the fluorescence emission. The fluorescence anisotropy, r, is defined as... 

Figure 4.9 illustrates time-gated imaging of rotational correlation time. Briefly, excitation by linearly polarized radiation will excite fluorophores with dipole components parallel to the excitation polarization axis and so the fluorescence emission will be anisotropically polarized immediately after excitation, with more emission polarized parallel than perpendicular to the polarization axis (r0). Subsequently, however, collisions with solvent molecules will tend to randomize the fluorophore orientations and the emission anistropy will decrease with time (r(t)). The characteristic timescale over which the fluorescence anisotropy decreases can be described (in the simplest case of a spherical molecule) by an exponential decay with a time constant, 6, which is the rotational correlation time and is approximately proportional to the local solvent viscosity and to the size of the fluorophore. Provided that... 

One can employ linearly polarized light to excite selectively those fluorophores that are in a particular orientation. The difference between excitation and emitted light polarization changes whenever fluorophores rotate during the period of time between excitation and emission. The magnitude of depolarization can be measured, and one can therefore deduce the fluorophore s rotational relaxation kinetics. Extrinsic fluorescence probes are especially useful here, because the proper choice of their fluorescence lifetime will greatly improve the measurement of rotational relaxation rates. One can also determine the freedom of motion of the probe relative to the rotational diffusion properties of the macromolecule to which it is attached. When held rigidly by the macromolecule, the depolarization of a probe s fluorescence is dominated by the the motion of the macromolecule. 

Due to the mixed polarization of monochromatized synchrotron radiation, the angle dependence of photoelectron emission as expressed in equ. (1.30) for completely linearly polarized light requires modification. This is considered in detail in Section 9.1, but the implication for the corresponding appropriate experimental set-up is treated in the next section. 

This expression disentangles the properties of the light polarization (coefficients /9, ( 1)), the geometry of two-electron emission (coefficients B t2(Ka, Kb)) and the dynamical parameters of the double photoionization process (coefficients A(ku k2, k)). The pkq(El) are the statistical tensors of the incident light which describe its polarization properties in the electric dipole approximation represented by 1. For linearly polarized light in which the electric field vector defines the z-axis of the coordinate frame, one has only two non-vanishing components given by (see equ. (8.99b))t... 

Figure 4.43 Energy- and angle-resolved triple-differential cross section for direct double photoionization in helium at 99 eV photon energy. The diagram shows the polar plot of relative intensity values for one electron (ea) kept at a fixed position while the angle of the coincident electron (eb) is varied. The data refer to electron emission in a plane perpendicular to the photon beam direction for partially linearly polarized light (Stokes parameter = 0.554) and for equal energy sharing of the excess energy, i.e., a = b = 10 eV. Experimental data are given by points with error bars, theoretical data by the solid curve.

Figure 4.45 Illustration of the content of equ. (4.90) which describes the angular distribution of Auger electrons (eb) in coincidence with the preceding photoelectron (ea). The data refer to 2p3/2 ionization of magnesium by linearly polarized photons of 80 eV and subsequent L3-M1M1 Auger decay, with emission of both electrons in a plane perpendicular to the photon beam direction. The alignment tensor a,

Figure 4.46 Energy- and angle-resolved patterns for two-electron emission in the two-step process of 2p3/2 photoionization of magnesium with subsequent L3-M, M, Auger decay induced by 80 eV photons with linear polarization (electric field vector along the x-axis). Both electrons are detected in a plane perpendicular to the photon beam direction the direction of the photoelectron (ea) is fixed at ( ) a = 180° and (b) = 150°, while the...

Figure 5.33 Spatial views of angle-resolved intensity patterns for the coincident emission of 4d5/2 photo- and N5-02>302 3 S0 Auger electrons in xenon caused by linearly polarized photons of 94.5 eV (electric field vector along the x-axis). (a) Fixed position of the photoelectron (e,) with (i) 0 = 90°, = 180° and (ii) 0 = 90°,

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