Dichroic fibers

The elemental state of incorporated metal colloids in dichroic fibers was experimentally proven by early X-ray studies [39, 40]. The diffraction patterns... 

The orientation of crystallites in PET fibers can also be assessed quantitatively by means of IR spectro-graphic examination. In this case, the basis for the assessment are the values of dichroic ratio (R) of the crystalline absorption bands in the fiber spectrogram. The determination of the values of fc is made using Fraser s dependence [24,25] modified by Chranowski [26] ... 

The 6 Nd YAG lasers pump the DM0, preamplifier and power amplifier (Fig. 19, Friedman et al., 1998). The YAG lasers are built from commercially available flashlamp/laser rod assemblies, acousto-optic Q-switches and frequency doubling crystals (LBO and KTP). Most of the mirror mounts and crystal holders are commercial. Nd YAGs are frequency doubled to 532 nm using a nonlinear crystal. The Nd YAG rod and nonlinear crystal are both in the pump laser cavity to provide efficient frequency conversion. The 532 nm light is coupled out through a dichroic and fed to multimode fibers which transport the light to the DM0 and amplifier dye cells. 

M, dichroic mirror P, dispersive prism I, iris L, lens T, 5-axis fiber positioner PUT 1, detection photomultiplier tube ... 

IR spectroscopy is not only useful for determining the chemical constitution of polymers. It additionally provides profound information on chain orientation and on the orientation of attached lateral substituents of polymers. In this case, polarized IR radiation is applied which is only absorbed by an IR-active bond if the plane in which the electrical field vector E of the IR beam oscillates is parallel to the transition dipole moment p of the vibration to be excited. If, on the other hand, the transition dipole moment p is perpendicular to the electrical field vector E of the IR beam no absorption is observed. Using this effect, the degree of orientation of a polymer sample (film, fiber) can be estimated by comparing the intensity at maximum /(11) and at minimum I ) absorption, i.e., the dichroic ratio. 

In the above instances the qualitative polarization characteristics of a band served to provide information of importance in making assignments. If we make use of the quantitative aspects of the dichroic ratios of absorption bands then we can in addition obtain structural information about the polymer. In particular, it becomes possible to determine in many cases the direction which transition moments make with the fiber axis, which is often significant in establishing structural parameters. It must be noted that transition moment directions do not by themselves always serve to specify the orientation of chemical groups. In cases where... 

It has been shown (Beer (72)] that under certain circumstances it is permissible to consider a polymer specimen as made up of a fraction,/, of fully oriented chains (i. e with molecular axis exactly parallel with the fiber axis) and the remainder, 1 — /, of randomly oriented chains. The necessary condition is satisfied by axially oriented polymers, regardless of the specific nature of the distribution of chains. A convenient relationship between /, the observed dichroic ratio R, and the dichroic ratio of perfectly oriented chains R0= is given as follows (Fraser (59)]. In an axially oriented specimen the extinction coefficient in a given direction for the unoriented portion is simply related to en and ea for the oriented portion. Since the total extinction coefficient for the latter is given by e - 2 F,a, the extinction coefficient for the unoriented portion in a given direction is... 

Fig. 5. Scanning confocal optical microscopy for single-molecule detection. Sample scanning configuration. The fiber exit and the active area of the SPAD serve as confocal pinholes. S sample, O high-NA microscope objective, DM dichroic mirror, L1,L2 lenses, F Filters.

A dichroic beam splitter separates the reflected spectrum into a portion near the resonance and a portion away from the resonance and directs the portions to two separate photodiodes. The electronic ratio of these two signals cancels most of the fiber transmission noise and provides a stable hydrogen signal. 

In 1958, Beer et al. re-examined the infrared dichroism situation and remeasured the dichroic ratio for several of the peptide bands in collagen. On the basis of studies on model compounds, they calculated the directions of the transition moments for the principal bands in the peptide link and, using the atomic coordinates for various proposed collagen models, the inclination of these transition moment vectors to the fiber axis. Since Beer (1956) had shown that the dichroism of a partially oriented polymer may be considered equivalent to that of a sample containing fully aligned and completely random portions, a disorientation parameter (/) characteristic of the degree of order of the sample could be calculated for each band. The spread of the values obtained for this parameter, which is characteristic of the sample only and not of the bands used to determine it,... 

Another investigation of hydrated collagen has been conducted by Fraser and MacRae (1959) who concluded on the basis of infrared dichroic measurements that the bound water molecules are primarily singly bonded to the —C=0 groups which project radially outward from the collagen molecules. The bound water molecules seemed to be preferentially oriented normal to the fiber axis. 

Figure 4 (bottom) shows the configuration of the optics to irradiate the seawater and to detect the subsequent signal through the window. A set of lenses, and L2, focuses the fiber image on the water channel. (The diameter of the laser beam at the measuring position was determined to be about 0.6 mm.) The fluorescence emitted and the light scattered in the focused volume are collected by the lens L3 on the surfaces of the fibers F1 and F2 with a two-to-one reduction factor. A dichroic filter transmits the fluorescence radiation to the fiber F j and the scattered radiation to the fiber F2. 

Cho, L.L., Reffiier, J.A. and Wetzel, D.L. (1999) Forensic classification of polyester fibers by infrared dichroic ratio pattern recognition./. Forensic Sci., 44 (2),... 

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