Reflectivity and Raman scattering

A schematic of a PL system layout is shown in Figure 5. This optical system is very similar to that required for absorption, reflectance, modulated reflectance, and Raman scattering measurements. Many custom systems are designed to perform several of these techniques, simultaneously or with only small modifications. 

The most often used detection method for the optical sensors are based on absorption, luminescence, reflectance, and Raman scattering measurements. The basic theory and instrumentation of most of these... 

The temperature dependence of the soft mode Eq. (5.76) has been studied in several oxide perovskites (among them in SrTiOs, BaTi03, PbTiOs and KTa03) by the neutron scattering, infrared reflectivity and Raman scattering (Fig. 5.14). 

In the following we describe the insights that optical spectroscopies, most particularly infrared reflection and Raman scattering, convey about this interplay and the rich phase behavior exhibited by these materials. 

One can distinguish between methods in which absorption of the evanescent surface wave in different wavelength regions is measured (these are often called attenuated total reflection methods), and methods which use the evanescent wave to excite other, spectroscopic phenomena, like fluorescence and Raman scattering or light scattering. As the methods of conventional fluorescence spectroscopy have been shown to be exceptionally successful in studies of proteins and other biopolymers, their evanescent surface-sensitive counterparts will be reviewed first. 

Figure 17. Reflectivity (O) and Raman scattering intensities (9) for an Al-AlOx-4-pyridine-COOH-Ag tunneling junction prepared on a diffraction grating substrate, as a function of the angle between the incident laser beam and the normal to the grating surface (45). At the same angles that absorption by surface plasmons causes reflectivity dips, the Raman signal shows peaks.

Note The estimations are carried out using optical reflectance (< ), magneto-oscillation (m), spin susceptibility (s), and Raman scattering (r). 

A. Seas and C. Christofides, Transmission and Reflection Spectroscopy on Ion Implanted Semiconductors A. Othonos and C. Christofides, Photoluminescence and Raman Scattering of Ion Implanted Semiconductors. Influence of Annealing... 

The principal techniques employed in the study of molecular vibrations and lattice dynamics are Raman, infrared (absorption and reflection), and neutron scattering. Numerous publications detail the theory and applications of the techniques [102,113]. Data for metal azides were obtained by a concerted use of all the techniques, and a brief discussion of their complementary character follows. 

The experiments which provide direct infonnation on the vibrations of one- and tridimensional lattices are infrared absorption (reflection) spectra, Raman scattering and neutron scattering. For a general discussion on the theoretical principles and experimental methods the reader is referred to the abundant literature on these... 

The inversion notation has become standard for a number of good reasons. In the Hermann-Mauguin terminology, the center of symmetry is dropped and the inversion axes maintained. In the Schonflies terminology, the center of symmetry is a key element and all the mirror reflections and simple or inversion rotation axes are dropped and replaced by other symbols these are described in Section V, as they are important in relation to site symmetry, group theory, and Raman scattering. 

FIGURE 2 An illumination of typical pump-probe technique used In ultrafast spectroscopies. The delay time between the pump and probe pulses is controlled by varying the difference of path length of two laser pulses. The measured signal can be the linear or nonlinear reflection/transmission, Raman scattering, luminescence, or any other signal from the probe pulse. 

Figure 2 illustrates the basic concept of a typical pump-probe spectroscopy used in most ultrafast spectroscopy techniques. In its simplest form the output pulse train of an ultrafast laser is divided in two by a beam splitter. One pulse in train (called pump) first excites the sample under investigation. The second pulse train (called probe) will probe the sample with a suitable time delay with respect to the pump by introducing an optical delay in its path and some optical property (e.g., reflectivity, absorption, Raman scattering, luminescence, optical nonlinear responses) of the sample is then detected to investigate the changes produced by the pump. In most of the time-resolved pump-probe experiments, the time resolution is limited only by the pulse width of the laser or the jitter between the laser systems. 

However, some polymeric samples contain crystallites or voids comparable in size to the visible wavelengths of the laser. These crystallites or voids scramble the incident laser polarization and thereby prevent any useful measurement of depolarization ratios. Some error in Raman polarization measurements arises because the incident light and Raman scattered light are multiply reflected at the surface of the sample and are also refracted upon entering or leaving the sample. The light-polarization directions are therefore poorly defined. Immersing the sample in a liquid that has a refractive index close to that of the polymer helps to minimize this problem [4],... 

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