Undulator polarizing

Accurate experimental determinations require that not only the handedness of the produced light, but its exact degree of polarization, are known. The theoretical performance of an undulator may be in practice be degraded by magnetic defects, and the optical beam can be further depolarized by reflections along the beamline. Again, the dephasing on optical elements can in principle be... 

Figure 12. The degree of circular polarization i3 measured behind the experimental chamber on two optically similar branches fed by the same undulator pair of the UE56/2 beamUne at BESSY II. Data taken from Ref. [55].

The SU5 beamline [89] at the Super-ACO synchrotron (LURE, Paris ) employed an electromagnetic undulator to produce fully variable polarization in the VUV region [83, 90, 91]. This beamline was equipped with a gas filter for the suppression of unwanted higher order radiation [92] and had a VUV polarimeter [93] permanently installed just before the experimental chamber that could be rapidly lowered into the beam for polarization determinations. Full polarization analyses had been performed in commissioning, with 53 values ranging from 0.9 to 0.96 for rep and from 0.9 to 0.99 for Icp [93]. The remainder was determined... 

The stability analysis [32] of the lamellar (one-dimensional) structure shows that it is stable only for weak coupling between the splay of polarization and molecular tilt. When Kv is larger than some critical value, layers start to undulate. 

Numerical results show that the reduction of the cone angle in the region of the unfavorable splay is smaller in the general tilt structure than in the structure with polarization being perpendicular to the tilt plane. The cone angle reduction is coupled to the undulation of layers. So in the general tilt structure the undulation is less pronounced than in the regular Blrev phase (Fig. 13), as was indeed observed experimentally [25]. 

Undulator radiation also has specific polarization properties, e.g., the fundamental radiation of a plane undulator as shown in Fig. 1.9 is completely linearly polarized, an undulator with helical magnetic structure produces circularly polarized light, and two crossed plane undulators with a dispersive section between them are capable of producing optional polarization which depends on the phase shift introduced by the dispersive element. 

Insertion devices, such as wigglers and undulators, that provide periodic magnetic arrays for modification of particle trajectories. These insertion devices may be used to alter spectral brilliance distribution, to produce intense peaks at certain photon energies or to generate circularly polarized radiation. 

By combining the thermal undulations of membranes with the polarization model it is shown that an increase in... 

One interesting questions is why the membranes never collapses, even when the undulations might drive part of than at separations less than 1 A. One possible explanation is provided by the strong, hard-wall like, Bom repulsion between the surface dipoles and their bound water molecules. Another possible explanation is that the polar headgroups of the neutral lipid bilayers, being hydrophilic, are more closely related to water than to the hydrocarbon region of the bilayers. Therefore, the van da Waals interaction between neutral bilayas might be betta described by [16] ... 

Fig. 7. Experimental values for the osmotic pressure as a function of separation distance from Ref. [13] (stars water, circles 1 M KC1 triangles 1 M KBr) are compared with calculations that combine the polarization model for hydration forces with the statistical treatment of the undulation, for the following values of the parameters = 9 Debyes, A = 60 A , A = 1 A, o = 0,...

Some attention has to be given to the degree of circular polarization y and thus to the creation of cpl. Two experimental principles are common the use of a quarter wavelength plate and the use of a Fresnel rhomb or a Solcil-Babinet compensator in a few experiments, radiation from a cyclotron after passage through a polarizing undulator was used. The degree of circular polarization is easily jeopardized when a X/4 plate is employed, as this is an interference device... 

Polarity, or action and reaction, we meet In every part of nature in darkness and light in heat and cold in the ebb and flow of waters In male and female in the inspiration and expiration of plants and animals In the systole and diastole of the heart in the undulations of fluids, and of sound in the centrifugal and centripetal gravity in electricity, galvanism and chemical affinity. 

The polarization factor, P, is usually known it depends on the radiation source and is closer to 1 for insertion devices such as wigglers or undulators as compared to bending magnets. The intensity, I, is measured as a function of 0 for many incident angles. Equation 4.2.1 can therefore be reduced to a linear fit of I vs. cos 0, where the slope and intercept can be transformed into the two remaining unknowns, A and a. 

---