Vertically polarized light

Figure 10,5 Definition of the variables used to describe the electric field produced by the oscillation of the charge q under the influence of vertically polarized light. (Reprinted from Ref. 2, p. 164.)...

The subscript v is attached to both of these intensities as a reminder that the foregoing analysis is based on the assumption of vertical polarization for the incident light beam. The ratio of these intensities gives the fraction of light scattered per molecule by vertically polarized light ... 

Since the vertically polarized light postulated in the derivation of Eq. (10.25) involves both the z component of the electric field and the angle 0, it is... 

The slope-intercept ratios have units of cubic centimeters per gram, and the intercepts are c/R where the subscript v indicates vertically polarized light. In this case Ky = 47t (n "/dc2The following values of n and dn/dc2 can be used to evaluate Ky ... 

Fig. 19. Hypothetical orientation of the SO - SI transition dipoles (blue band) of the bluelight photoreceptor in the Phycomyces sporangiophore as concluded from polarized light experiments96). Horizontally polarized light is about 20% more effective than vertically polarized light, as sketched...

It is easy to show that rn = r/2. Therefore, the emission anisotropy observed upon excitation by natural light is half that upon excitation by vertically polarized light. In view of the difficulty of producing perfectly natural light (i.e. totally unpolarized), vertically polarized light is always used in practice. Consequently, only excitation by polarized light will be considered in the rest of this chapter. 

Such a crystal is double refracting since the two values of the refractive index will cause the two polarizations to propagate along different paths. Separation of the two polarizations occurs at the interface where the horizontally polarized light is totally internally reflected. The vertically polarized light, on the other hand, is transmitted across the interface where the second half of the polarizing cube returns this polarized beam to its... 

Vv and Vh are fluorescence intensities of vertically and horizontally polarized components, respectively, obtained with vertically polarized light, g is the correction factor and is equal... 

Mie theory for horizontally and vertically polarized light. Polystyrene spheres were used for calibration. 

Substituting this expression for the molecular polarizability a into Eq. (1.83) gives the intensity per unit scattering volume of vertically polarized light scattered in the horizontal plane ... 

Fluorescence Polarization Studies of PMA and PAA. Time-resolved fluorescence polarization measurements are potentially a powerful means for studying molecular mobility. The fluorescence anisotropy function r(t) may be generated by monitoring the decay of vertically (Iv(t)) and horizontally (Ijj(t)) polarized components of emission following excitation by vertically polarized light pulses (Equation 1). 

The general expression for the scattering form factor of randomly oriented particles and vertically polarized light reads ... 

The Rayleigh-Debye-Gans differential scattering cross section in the scattering plane for vertically polarized light (Eigure 14.1) is... 

Steady-State Anisotropy Following continuous excitation with vertically polarized light, a distribution of fluorophores whose transition vectors for the absorption process are vertically aligned will be photoselected, creating an excited state population, which possesses a degree of anisotropy (r) or optical order, in an otherwise isotropic distribution of fluorophores. Measurement of the intensity of fluorescence, via an emission polarizer in planes parallel (z n) and perpendicular (zx) to the vertical plane allows estimation of r from... 

Fig. V-20. The indicatrixes of Rayleigh light scattering lz is the total intensity of the scattered light /H0R and /VERT are the intensity of horizontally and vertically polarized light, respectively I u and I are the intensities of unpolarized and polarized light, respectively...

In a practical experiment, a correction factor is introduced to take into account the sensitivity of the fluorescence spectrometer to anisotropy. The factor G = /hv//hh is used, where the subscript v and h correspond to the vertically polarized light (z direction) and the horizontally polarized light (x- and -axes), respectively, with the incident light polarized in the.v direction. Taking this correction factor into account, the value of the fluorescence anisotropy ratio is... 

With vertically polarized light, the parallel Iw (t) and perpendicular Lh (t) components of the fluorescence intensity at time after the start of the excitation are... 

Vv and Vh are the intensities of the vertically and horizontally polarized components, respectively, of the fluorescence elicited by vertically polarized light, g is the correction factor and is equal to Hy / Hh where Hy and Hh ai e the verticaljy and horizontaljy polarized components, respectively, of the fluorescence elicited by horizontaljy polarized light. 

Figure 5.17. Time-correlated single photon couming traces acquired under equilibrium folding conditions with 10 pM aTS and 10 / M ANS. The vertical and horizontal polarization components of the ANS excited-state decity are shown at 0 M (a, vert cal b, hor zontal) and 3 M urea (c, vertical d. horizontal) upon excitation with 370 nm vertically polarized light. 1 he fast component corresponds to the decay of unbound ANS. The corresponding calculated anisotropy curves at 0 and 3 M (solid and dotted trace, respectively] are also shown (inset). The smooth lines represent fits to the associative model Source Bilsel. O., Yang. L. Zitzewitz, J. A, Beechem. J. M. and Mattliews, C. R. 1999, Biochemistry. 38.4177 — 4187. Authorization of reprint accorded by the American Chemical Society.

When excitation was performed with a vertical polarized light, whether on solution of ai- acid glycoprotein or on the crystal, the band widths of the spectra are 10 nm smaller than those observed when the spectra were recorded with unpolarized light. In the crystal, the bandwidth is equal to 35 1 nm instead of 43 1 nm, and in solution, it is equal to 41 1 nm instead of 54 1 nm. We do not know whether this phenomenon is due to the polarizer used or not. 

This expression for K is valid for vertically polarized light. In what follows in this chapter, we assume that the incident field is vertically polarized and that we are observing in the plane of incidence, that is, sin O = 1. For light that is polarized horizontally. Equation 18.17 should have a factor cos 0, and for unpolarized light, the factor should be (1 -I- cos 2 eyi. 

The timescale of fluorescence emission is comparable to that of rotational diffusion of proteins and the timescale of segmental motions of protein domains or individual amino acid residues. The polarization or anisotropy of the emission provides a measure of these processes. Suppose a sample is excited with vertically polarized light (Fig. 11), and that the sample is viscous so that the fluorophores do not rotate during the lifetime of the excited state. Then the emission is polarized, usually also in the vertical direction. This polarization occurs because the polarized excitation selectively excites those fluorophores in the isotropic solution whose absorption... 

Static light scattering (SLS) was performed with a Fica-50 photometer using vertically polarized light (A = 436 and 546 nm). A correction was made for scattering of the solvent. The Rayleigh-Gans-Debye... 

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