Polarization background subtraction

Integral intensities were obtained after dead-time corrections, background subtraction and normalization to averaged monitor counts. The Lp correction was applied in the usual way. Since the polarization ratio was not measured at BW5 so far, 90% linear horizontally polarized radiation was assumed for all scans. Calculations show that even a change in the beam polarization of 10% would effect the intensities of the highest order reflections of less than 1.5%. 

Figure 8.3. LORENTZ-polarization corrected WAXS curve of poly(3-dodecylthiophene) before and after background subtraction (from PROSA et al. [109]). The authors define q in the way that is identical to the definition of s in this book...

Both spectral and polarization discrimination of the background subtracted signals are trivial to implement (see Figure 3.16). Standard dichroic filters are available for all common dye pairs and inexpensive polarization beam splitters are commonly available from optical component manufacturers. 

Figure 10. Polar angle ( f) dependence of the (003) and (310) planes of the 80/20 PI/PEI molecular composites at the draw ratio of 3.5. The line with dots represents the (003) plane after background subtraction.

In video microscopy, for instance, background is normally subtracted using differential interference contrast (DIC) [18]. This technique, which requires a number of manipulations from the user, may now be automated using a new method called polarization-modulated (PMDIC) [19,20], It requires the introduction of a liquid crystal electro-optic modulator and of a software module to handle difference images. PMDIC has been shown to bring improvements in imaging moving cells, which show a low contrast, as well as thick tissue samples. 

Figure 6.10. ARUPS spectra taken on a TTF-TCNQ thin fllm at F 100 K and with 21.2 eV photons along the directions bisecting both a- and -directions (polar angles 0 are shown). A parabolic background has been subtracted to enhance the features. Reprinted from Surface Science, Vol. 482 85, C. Rojas, J. Caro, M. Grioni and J. Fraxedas, Surface characterization of metallic molecular organic thin films tetrathiafulvalene tetracyanoquinodimetane, 546-551, Copyright (2001), with permission from Elsevier.

For horizontally polarized excitation light, and Ihh are the intensities of the vertically and horizontally polarized fluorescence emissions, respectively. It is strongly recommended to use the background-corrected intensity values for the calculations. The background correction is determined by subtracting the intensity value obtained for the buffer with a certain polarizer setting from the intensity value for the sample obtained with identical settings. 

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