Angular Birefringence

Bulk potassium niobate (KNbOs) is well suited to our needs, beeause birefringent type-I non-critical phasematehing (NCPM) can be exploited for highly efficient SHG of 850 nm at room temperature . This NCPM avoids any spatial waUc-off between the fundamental and second harmonic beams, as well as maximizing the angular acceptance of the phasematching process. 

Fig. 2.5. Steady-state and dynamic oscillatory flow measurements on a 2 wt. per cent solution of polystyrene S 111 in Aroclor 1248 according to Philippoff (57). ( ) steady shear viscosity (a) dynamic viscosity tj, ( ) cot 1% from flow birefringence, (A) cot <5 from dynamic measurements, all at 25° C. (o) cot 8 from dynamic measurements at 5° C. Steady-state flow properties as functions of shear rate q, dynamic properties as functions of angular frequency m. Shift factor aT which is equal to unity for 25° C, is explained in the text, cot 2 % and cot 8 are expressed in terms of shear (see eqs. 2.11 and 2.22)...

It is evident that the contributions due to angular movements are caused by diffusion forces corresponding to the state of orientation, whereas the radial component is a hydrodynamic contribution. The radial force, as exerted by the flowing solvent, is balanced by the rigidity of the rod and has no consequences for the birefringence of orientation. According to eqs. (5.15), one obtains for rigid dumb-bells ... 

It is worth pointing out that in low-7(, PR materials with molecular birefringence as the dominant contribution to the index modulation, the real response time and the PR sensitivity can also be limited by the diffusion time of angular rotation of the chromophores under the drive of the space-charge field, and even the time constant xe for the formation of the space-charge field may be smaller [27],... 

Figure 22. Refractive index modulation as a function of the external angle of the probe beam with respect to the sample normal for the material given in [20], when the writing beams are arranged at a constant 55° and 75° to the sample normal. A) angular variation if reorientational birefringence is dominant B) angular variation if Pockels response were the primary source of index contrast.

Another mechanism responsible for the optically induced anisotropy is angular redistribution (AR) of molecules. This mechanism has been widely developed to explain photoinduced birefringence and dichroism. In most experimental cases, there is evidence of some rotation of molecules during the photoisomerization cycle (see Reference 2, for example). This rotation results in AR, because the molecules remain longer in states with lower excitation probability, and so more molecules are accumulated perpendicular to the pump polarization. The AR process is initiated by the AHB, and these two processes should be studied simultaneously in the framework of general... 

The flow birefringence of actomyosin is appreciably higher than that of L-myosin (Szent-Gyorg5d and coworkers, 1942 Schramm and Weber, 1942), but has not yet been measured under quantitatively defined conditions greater too are the turbidity due to light scattering (Portzehl et al., 1950) and the angular dissymmetry (Jordan and Oster, 1948 Mommaerts and Parrish, 1951). The turbidity of a 1% solution is about 0.5 cm. X-Ray studies have introduced no new concepts since the discussion by Bailey (1944). 

Light Scattering Loss of Zero-Birefringence Copolymer. Table II shows the scattering parameters of zero-birefringence poly(MMA-co-BzMA) and those of the homopolymer glasses. The Vy and Hy intensities of all samples had no angular... 

I. Clear, colorless, angular crystals with a low birefringence, identified as tricalcium silicate... 

Polymers may exhibit a biaxial orientation. The segmental orientation function is in this case a function of two angular variables, i.e. /(, v), as shown in Figure 10.7. The in-plane orientation is different in the zx and zy planes (Figure 10.7). There are several methods commonly used to determine chain orientation in-plane birefringence, wide angle X-ray diffraction, small angle X-ray diffraction, infrared spectroscopy and sonic modulus measurements. In the case of uniaxial orientation there is only... 

The stiffness of the chain can be obtained by measuring a value for (which is a mean square end to end distance for a chain) by angular light scattering of a dilute polymer solution or simultaneous stress and birefringence measurements on a solid polymer in its rubbery state. The stiffness z is then... 

The field distorts the cubic lattice and results in a change in the angular (or spectral) positions of the Bragg reflections. Moreover, field-induced phase transitions into novel phases have been observed [91, 96]. The field can also induce birefringence parallel to the field direction due to the optical biaxiality of the distorted cubic lattice [97]. 

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