Light interactive characteristics

The green colours in the northern lights come from the interaction of accelerated electrons with oxygen atoms. The red colours usually come from nitrogen atoms. How do these interactions lead to atoms of different elements emitting light with characteristic wavelengths ... 

We can see the hierarchy of optical near-fields and far-fields because optical near-field interactions are distinguishable with propagating light. This characteristic feature has led to hierarchical optical system designs, such as nanophotonic hierarchical holograms (Tate et al., 2008), where independent functions are associated with both optical near- and far-fields in the same device. Figure 3 shows the basic concept of the hierarchical hologram. 

The microscope has been associated with forensic science ever since Locard and Sherlock Holmes. The study of microscopy provides a foundation for study of spectroscopy. Simple microscopy is based on the interaction of visible light with matter, whereas spectroscopy is broadly defined as the interaction of electromagnetic energy with matter. Once visible light interacts with a sample, that light carries information about the physical and chemical characteristics of the sample. The same is true in all modes of spectroscopy. The detector in a microscope is the human eye and the characteristic that is most studied is color, but color is an expression of frequency and wavelength, characteristics exploited across the electromagnetic spectrum. 

Besides intensity and energy, another characteristic of light that can be affected when light interacts with matter and can, thus, be used on the characterization of materials is its polarization. The best known technique that uses the polarization of light to characterize materials is the ellipsometry. In ellipsometry we measure the change on the state of polarization of light upon reflection by or transmission through a sample, which depends on its complex dielectric function. 

The ability of SPR to probe both kinetic and thermodynamic processes, as well as to provide micro-structural information, make it a very important component of the experimental methodology available to probe molecular interactions occurring at surfaces. Furthermore, it allows some of the limitations of other techniques to be overcome. For example, other methods often require one of the partners to be labelled in some way in order to allow it to be detected. Fluorescent probes, radioactive labels, and attachment of independently detectable molecules (e.g. enzymes) have all been used for this purpose. These suffer from the drawback that they may interfere with the binding of the labelled partner to the unlabelled one, or cause unwanted structural perturbations. SPR observations can be based solely on the dielectric properties of molecules, or their intrinsic light absorption characteristics, and thus require no specific labelling. 

Passive all-optical switching, also known as nonlinear self-action effects, offers a practical solution to such challenges. In these processes, the incident light interacting with the nonlinear optical material creates the complex phase shift necessary to change its polarization state, transmission, and other spatio-optical characteristics. 

Spectroscopy, or the study of the interaction of light with matter, has become one of the major tools of the natural and physical sciences during this century. As the wavelength of the radiation is varied across the electromagnetic spectrum, characteristic properties of atoms, molecules, liquids and solids are probed. In the... 

Laser Doppler Velocimeters. Laser Doppler flow meters have been developed to measure Hquid or gas velocities in both open and closed conduits. Velocity is measured by detecting the frequency shift in the light scattered by natural or added contaminant particles in the flow. Operation is conceptually analogous to the Doppler ultrasonic meters. Laser Doppler meters can be appHed to very low flows and have the advantage of sensing at a distance, without mechanical contact or interaction. The technique has greatest appHcation in open-flow studies such as the deterrnination of engine exhaust velocities and ship wake characteristics. 

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