Optical diffraction method

Optical diffraction methods. 2. The transform method. It is not absolutely necessary to make multiple pattern of many repetitions of the unit cell projection it is possible to obtain the desired information (the relative intensities of the diffracted beams corresponding to X-ray reflections) from the diffraction pattern given by a group of points representing the atoms in one unit cell. The possibility of doing this is indicated by the following consideration. 

Graphical methods and machines for evaluating structure amplitudes 286 Optical diffraction methods ... 

In this chapter we review some of the most important developments in recent years in connection with the use of optical teclmiques for the characterization of surfaces. We start with an overview of the different approaches available to tire use of IR spectroscopy. Next, we briefly introduce some new optical characterization methods that rely on the use of lasers, including nonlinear spectroscopies. The following section addresses the use of x-rays for diffraction studies aimed at structural detenninations. Lastly, passing reference is made to other optical teclmiques such as ellipsometry and NMR, and to spectroscopies that only partly depend on photons. 

Dederichs, P.H. (1972) Dynamical diffraction theory by optical potential methods, Solid State Phys., 27, 125. 

Synthesis of the first mesoionic nematic and smectic A liquid crystals derived from sydnones has been described and their self-organization into liquid crystal phases has been studied by optical, calorimetric, and powder X-ray diffraction methods <2005CC1552>. 

Experimental equipment for X-ray diffraction methods has improved enormously in recent years. CCD detectors and focusing devices (Goepel mirror) have drastically reduced the data acquisition time. Cryogenic systems have been developed which allow structural studies to be extended down to the liquid helium temperature range. These developments have had important implications for SCO research. For example, fibre optics have been mounted in the cryostats for exploring structural changes effected by light-induced spin state conversion (LIESST effect). Chaps. 15 and 16 treat such studies. 

The structure of films has been studied by several methods, such as X-ray diffraction, IR spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, although the simplest and least expensive technique is that of optical diffraction measurements. 

The various techniques available for structural characterization may be grouped under the following categories optical methods, diffraction methods, electron microscopic... 

An interesting aspect of many structural phase transitions is the coupling of the primary order parameter to a secondary order parameter. In transitions of molecular crystals, the order parameter is coupled with reorientational or libration modes. In Jahn-Teller as well as ferroelastic transitions, an optical phonon or an electronic excitation is coupled with strain (acoustic phonon). In antiferrodistortive transitions, a zone-boundary phonon (primary order parameter) can induce spontaneous polarization (secondary order parameter). Magnetic resonance and vibrational spectroscopic methods provide valuable information on static as well as dynamic processes occurring during a transition (Owens et ai, 1979 Iqbal Owens, 1984 Rao, 1993). Complementary information is provided by diffraction methods. 

Conclusion. This book is concerned with optical and X-ray methods but there are of course other methods of studying the structures of crystals and molecules. The diffraction of electrons and of neutrons depends on the same general principles as that of X-rays or visible light but there are important theoretical differences, and the expert mental arrangements are very different. It is not proposed to deal with either of these subjects here, but a few remarks will be made on their relation to the X-ray diffraction method. 

Another optical technique, called the back-light scattering (Kossel-diffraction) method can also be used to investigate structure in food emulsions and foams. In this method, the emulsion (or foam) in a transparent vessel is illuminated by a collimated laser beam (See... 

SNOM combines the optical contrast with a high lateral resolution of SPMs [55,56]. Scanning a surface with a sharp optical fibre tip within the range of the optical near field makes it possible to overcome the optical diffraction limit that restricts the resolution of conventional optical microscopy. Moreover, the SNOM probe operates at a finite distance from the surface, so that damage and distortion of delicate samples can be eliminated. The drawback of SNOM compared to other SPM methods is its relatively low resolution - around tens of nanometers [62,63]. 

In this book, particles larger than 1 pm are of primary interest, and thus, only the Fraunhofer diffraction method, which can account for particles larger than 2-3 pm, is discussed here. The Fraunhofer diffraction theory is derived from fundamental optical principles that are not concerned with scattering. To obtain the Fraunhofer diffraction, two basic requirements must be satisfied. First, the area of the particle or aperture must be much smaller than the product of the wavelength of light and the distance from the light source to the particle or aperture. Second, this area must also be smaller than the product... 

Intermediate Alkali Feldspars. The alkali feldspars with intermediate composition vary in their TL signal when seen in detail. All of them differ significantly as a group from the end members. However, several interesting common features throw light on their overall behaviour. These features suggest a new means for identifying structure, which differs from the traditional optical and X-ray diffraction methods. 

---