Extinction ring

Fig. 18. Variations in average widths of the extinction rings with PCL content in ring-banded spherulites in PCL-PVC blends, calculated as ( ) (O) where n,...

For some polymers, such as polyethylene (37), it was shown that their lamellae have a screwlike twist along their unit cell b axis, on the spherulite radius. The distance corresponding to one-half of the pitch of the lamellar screw is just in accordance with the extinction ring interval visible on some photographs. 

In another study, banded spherulites of PHBV random copolymer were prepared by isothermal crystallization at 90 C for ten hours.Using tapping-mode AFM, the concentric periodic ridges and valleys on the surface of the banded spherulites of this polymer were found to consist of edge-on and flat-on lamellae, respectively. The periodic concentric ridges and valleys observed by AFM corresponded to the periodic extinction rings observed by polarized optical microscopy. AFM measurements showed that the interaction between the AFM probe and the sample surface can be significantly influenced by lamellar orientation. ... 

The UV-Vis absorption spectra of the homocyclic molecules S with n = 6-10, 12, 15, and 20 have been recorded in methylcyclohexane and/or methanol solutions at 20 °C in the range 200-360 nm [42]. Representative examples of the spectra are shown in Fig. 1. Their molar extinction coefficients (e) at 254 nm in methylcyclohexane solution linearly increase with the ring size as the following data demonstrate (20 °C) ... 

Figure 9.44 The common nitrogenous ring structures of cyanine-type dyes. Indolium-based dye derivatives are the most frequently used due to the high extinction coefficient of the indol groups.

In Fig. 14, the UV spectra of the domino oxidation products are shown. As the number of oxatetrasilacyclopentane rings increases, the lowest energy absorption maximum shifts bathochromically, and the molecular extinction coefficient becomes far larger (10 270 nm (s 3200), 11 273 nm (s 7600), 12 292 nm (s 25000), 13 297 nm (s 51900). The intense absorption of the order 104 is remarkable because these molecules contain no obvious chromo-phores which should give such intense absorption. Since the intense absorption is not observed in the ladder polysilanes, it is apparently due to the electronic effect of the oxygen atoms on the Si-Si a conjugation systems. 

For a microring resonator with a waveguide width of 5 pm and coupling gap of 200 nm, a resonance extinction ratio of 12 dB for TE polarization and 9 dB for TM polarization has been achieved, as shown in Fig. 2.10. The ring resonator had a race track shape with circular sections of 500 pm radius and straight coupling section of 100 pm in length. The width of the two exposed strips is about 50 pm. 

The ability to measure small index perturbations, (I/Ven. depends on the depth (i.e., the extinction ratio at resonance) and width of these resonances. The depth and width in turn depend on the relative values of the coupling coefficient t and the resonator loss a. Figure 9.16 shows typical ring resonator spectra calculated for two different loss values. The maximum extinction ratio is obtained at critical coupling when t = a, and the output intensity at resonance is exactly zero. The width of the resonances depends on the total round trip resonator loss, at, which is the product of waveguide losses within the ring (a) and coupling loss (t) at the coupler. 

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