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Propagation of light is described as the simple harmonic motion of transverse waves. Combining waves that propagate on orthogonal planes give rise to linear, elliptical, or spherical polarization, depending on their amplitudes and phase differences. Classical experiments of Huygens and Young demonstrated the principle of optical interference and diffraction. Generalization of Fraunhofer diffraction to scattering by a three-dimensional arrangement of atoms in crystals forms the basis of diffraction methods. Fresnel diffraction finds application in the design of zone plates for X-ray microscopy. Optical microscopy, with resolution given by the Rayleigh criterion to be approximately half the wavelength, works best when tailored to the optimal characteristics of the human eye (λ = 550 nm). Lenses suffer from spherical and chromatic aberrations, and astigmatism. Optical microscopes operate in bright-field, oblique, and dark-field imaging conditions, produce interference contrast, and can image with polarized light. Variants include confocal scanning optical microscopy (CSOM). Metallography, widely used to characterize microstructures, requires polished or chemically etched surfaces to provide optimal contrast. Finally, the polarization state of light reflected from the surface of a specimen is utilized in ellipsometry to obtain details of the optical properties and thickness of thin film materials.

Concentrated colloidal suspensions are a well‐tested model system which has a glass transition. Colloids are suspensions of small solid particles in a liquid, and exhibit glassy behaviour when the particle concentration is high; the particles are roughly analogous to individual molecules in a traditional glass. Because the particle size can be large (100 nm–1000 nm), these samples can be studied with a variety of optical techniques including microscopy and dynamic light scattering. Here the chapter reviews the phenomena associated with the colloidal glass transition, and in particular discuss observations of spatial and temporally heterogeneous dynamics within colloidal samples near the glass transition. Although this chapter focuses primarily on results from hard‐sphere‐like colloidal particles, it also discusses other colloidal systems with attractive or soft repulsive interactions

This chapter gives an overview of the main optical methods used to detect and study single molecules and other small objects (nano-objects). Much of the work so far has exploited the excellent sensitivity and selectivity of fluorescence, but several new techniques, mostly based on nonlinear optics, have recently reached the single-molecule or single-nanoparticle regime. The chapter briefly discusses some results with reference to published reviews. Single-molecule techniques have now been incorporated into the arsenal of the physico-chemist and the cell biologist. However, the recent development of super-resolution techniques and of new labels suggests that further progress can be expected from measurements on single nano-objects in the next few years.

Polymer science is, of course, driven by the desire to produce new materials for new applications. The success of materials such as polyethylene, polypropylene, and polystyrene is such that these materials are manufactured on a huge scale and are indeed ubiquitous. There is still a massive drive to understand these materials and improve their properties in order to meet material requirements; however, increasingly polymers are being applied to a wide range of problems, and certainly in terms of developing new materials there is much more emphasis on control. Such control can be control of molecular weight, for example, the production of polymers with a highly narrow molecular weight distribution by anionic polymerization. The control of polymer architecture extends from block copolymers to other novel architectures such as ladder polymers and dendrimers. Cyclic systems can also be prepared, usually these are lower molecular weight systems, although these also might be expected to be the natural consequence of step-growth polymerization at high conversion. Polymers are used in a wide range of applications, as coatings, as adhesives, as engineering and structural materials, for packaging, and for clothing to name a few. A key feature of the success and versatility of these materials is that it is possible to build in properties by careful design of the (largely) organic molecules from which the chains are built up. For example, rigid aromatic molecules can be used to make high-strength fibres, the most highprofile example of this being Kevlar®; rigid molecules of this type are often made by simple step-growth polymerization and offer particular synthetic challenges as outlined in Chapter 4. There is now an increasing demand for highly specialized materials for use in for example optical and electronic applications and polymers have been singled out as having particular potential in this regard. For example, there is considerable interest in the development of polymers with targeted optical properties such as second-order optical nonlinearity, and in conducting polymers as electrode materials, as a route towards supercapacitors and as electroluminescent materials. Polymeric materials can also be used as an electrolyte in the design of compact batteries.

This chapter presents the latest results demonstrating the flexibility and sensitivity of optical methods for the investigation of the physical properties of DWs in 3D. Domain walls in ferroelectric materials are nanoscale interfaces separating regions with different orientation of the polarization. They have long been considered as imperfections affecting the overall macroscopic properties of ferroelectrics. However, the recently discovered rich and diverse local physical properties of ferroelectric DWs have transformed these domain boundary regions into individual nanostructures with significant fundamental interest and potentially viable application in nanoelectronic device components. This chapter emphasizes the important contribution of both nonlinear and linear optical microscopy in different geometries (transmission, reflection, and non-collinear geometry) to access the detailed morphology of ferroelectric domain walls, obtain their 3D profile, access their internal structure, and establish correlations with their electronic properties.

This chapter begins by describing the beginnings of optical microscopy, marking the onset of revolution in biology. Microscopes display the depth of field and depth of focus of microscopic images by tracing the path of light waves from the focal plane to the image plane. the part of the microscope that produces the images is called the “lens” and producing variations on it would mean corresponding variations in images. Sample problems are also provided at the end of the chapter.