Berek compensators

Using a Berek compensator a value of 0 65 was found. This was felt to be too high and an attempt was made to determine the individual refractive indices using a Becke line assessment with immersion liquids of different refractive indices. The refractive index perpendicular to the fibre axis, was found to be in the range 1-63-1-64. The refractive index /."n parallel to the fibre axis, was very much more difficult to measure but... 

As expected, results in Fig. 15.3 show that significant fiber orientation is only achieved when the matrix is anisotropic. Similar conclusions can be drawn from birefringence measurements (made by the compensation method, using a Berek compensator) on composite films, as shown in Fig. 15.4. The birefringence is a measure of the degree of order of the matrix and therefore the good agreement between these data and those obtained from SALS (S) reveal the excellent compatibility between the matrix and the fibers, which results from a similarity between the chemical structure of both components of the composites. 

The investigation of the polarization characteristies of the gradient-oriented polymer films was carried out by means of a Berek compensator and a polarization microscope MIN-B (wavelength equals to 0,636pm (636nm), using a special fabrication laboratory [90],... 

S.9.4 The Berek Compensator. The Berek compensator (shown in Fig. 6.31) is a calcite (naturally birefringent crystal) plate, cut perpendicular to the optic axis, about 0.1 mm thick, that can be tilted about 20° by a graduated dial motion. In the null position (generally the 30° reading on the dial), the plate is horizontal and introduces no net retardation. A tilt, however, introduces a net retardation between the perpendicular vibrations of light. When viewing a stressed specimen, the user rotates the dial on either... 

For large values, the Berek compensator is a disk of uniaxial material cut on the basal plane (normal to the optic axis) and mounted on a ring which can be tilted about a horizontal axis. When horizontal it has no retardation when tilted, it can reach 2000nm if it is quartz and more than 50,000nm if it is calcite. 

We analyzed the molecular orientation of the parts using a polariscope and a polarizing optical microscope (POM, Olympus BX51-P) with a Berek compensator. In addition, a skin-shear-core structure of molded parts was analyzed by polarizing microscope after a thin section was cut paralleled to the MD from the molded parts with a microtome (Leica Microtome, 2055 Autocut, every 30 pm thickness). 

Amorphous isotropic PET film (confirmed using Berek compensation technique) of ca. 250 micron thickness were extruded fi om semicrystalline PET pellets tradenamed F80, IV0.82 supplied by Tergal Fibre, France. 

Figure 1 A schematic representation of a fairly advanced single-molecule setup. BS, beam splitter (nonpolatizing, polarizing, or a dichroic mirror) PD, fast photodiode POL, polarizer BE, beam expander BP, bandpass filter WP, quarter waveplate or Berek compensator EF, emission filter. If a dichroic mirror is used to split the emission between the APDs, then additional filters are usually placed in front of each APD to prevent leakage of the emission into the incorrect channel. The photodiode is only used in combination with pulsed excitation in the determination of the excited-state lifetime.

The fibers of the blends were reasonably transparent. The birefringence of the fibers was measured using a Leitz polarized microscope with a Berek tilting compensator (30-order) and a white light source. 

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