Dispersed birefringent phase

The contribution of dissolved surfactant, whose concentration was only 0.001M, compared to 7M of decane, to the observed Class I peaks must have been negligible. Class II peaks were not observed in Spectrum 13 of the birefringent phase, and Class I peaks were broadened (linewidth about 30 Hz) compared to the peaks in Spectrum 12 (linewidth less than 5 Hz). Therefore it seems quite possible that the dispersed birefringent phase did give Class I peaks in Spectrum 12, but that these peaks, due to either the surfactant or to absorbed decane or to both, merged with those of the decane in the isotropic phase. 

Figure 6. The guided mode dispersion curves for a birefringent film and an optically isotropic substrate. Both the fundamental and harmonic curves are shown. The TE mode utilizes the ordinary refractive index and TM primarily the extraordinary index. Note the change in horizontal axis needed to plot both the fundamental and harmonic dispersion curves. Phase-matching of the TEq(co) to the TMo(2o>) is obtained at the intersection of the appropriate fundamental and harmonic curves.

Nematic phase birefringence, which was observed in the cellulose solutions made from the 24.5/75.5 solvent, appeared immediately following dissolution and persisted throughout a two week period. The uniformly dispersed birefringent patterns were the most prevalent ones in the nematic solutions at all DPs studied, but Schlieren and thread-like patterns indicating nematic phases were readily observed in solutions of DP 450 cellulose. 

Polarizing microscopy identifies birefringent phases, for example liquid crystalline phases (17,18), and reveals dispersed particles, provided they are larger than about 1y (ultimate sensitivity is about 0.3y). 

H3uasi-phase matching (QPM), modal dispersion phase matching (MDPM), anomalous dispersion phase matching (ADP), and birefringent phase matching (BPM). 

The first and third order terms in odd powers of the applied electric field are present for all materials. In the second order term, a polarization is induced proportional to the square of the applied electric field, and the. nonlinear second order optical susceptibility must, therefore, vanish in crystals that possess a center of symmetry. In addition to the noncentrosymmetric structure, efficient second harmonic generation requires crystals to possess propagation directions where the crystal birefringence cancels the natural dispersion leading to phase matching. 

One may wish to pursue the bulk phase-matched behavior beyond the noncritical (8=w/2, 8 defined below) case. In bulk samples birefringence is the usual means to overcome the natural dispersion... 

Rotation of the polarization plane (or the axes of the dichroic ellipse) by a small angle a occurs when the phases for the two circular components become different, which requires a difference in the refractive index n (Pearlman and Nguyen 1991). This effect is called circular birefringence. The change of optical rotation with wavelength is called optical rotary dispersion (ORD). 

Sensitized for blue-green or red light, photoconductive polyimides and liquid crystal mixtures of cyanobiphenyls and azoxybenzene have been used in spatial light modulators [255-261]. Modulation procedure was achieved by means of the electrically controlled birefringence, optical activity, cholesteric-nematic phase transition, dynamic scattering and light scattering in polymer-dispersed liquid crystals. 

The final chapter on applications of optical rheometric methods brings together examples of their use to solve a wide variety of physical problems. A partial list includes the use of birefringence to measure spatially resolved stress fields in non-Newtonian flows, the isolation of component dynamics in polymer/polymer blends using spectroscopic methods, the measurement of the structure factor in systems subject to field-induced phase separation, the measurement of structure in dense colloidal dispersions, and the dynamics of liquid crystals under flow. 

Fig.4. Schematic representation of the different common phase-matching techniques in the k space representation. (ADM) anomalous dispersion (WBM) waveguide birefringence (MD) modal dispersion (QPM) quasi-phase-matching (C) Cerenkov and (CP) counter propagating Cerenkov...

Applications of visible light such as the use of polarized light, birefringence, retardation, angles of extinction, dispersion staining, and phase contrast will be explained, discussed and related primarily to asbestos with some discussion of quartz. 

Three of the experiments are completely new, and all make use of optical measurements. One involves a temperature study of the birefringence in a liquid crystal to determine the evolution of nematic order as one approaches the transition to an isotropic phase. The second uses dynamic laser light scattering from an aqueous dispersion of polystyrene spheres to determine the autocorrelation function that characterizes the size of these particles. The third is a study of the absorption and fluorescence spectra of CdSe nanocrystals (quantum dots) and involves modeling of these in terms of simple quantum mechanical concepts. 

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