Characters of Light

Schrodinger s equation is widely known as a wave equation and the quantum formalism developed on the basis thereof is called wave mechanics. This terminology reflects historical developments in the theory of matter following various conjectures and experimental demonstration that matter and radiation alike, both exhibit wave-like and particle-like behaviour under appropriate conditions. The synthesis of quantum theory and a wave model was first achieved by De Broglie. By analogy with the dual character of light as revealed by the photoelectric effect and the incoherent Compton scattering... 

The concept of dual character of light is particularly relevant to the discussion of optical sensors. In this introductory section, the basic quantized (corpuscular) aspects of light as they relate to optical sensors are reviewed first, followed by a brief review of physics of optical waveguides and optical fibers which rely on wavelike (continuous) properties of light. Detailed information can be found in analytical (e.g., Skoog et al., 1998) and specialized textbooks (e.g., Hollas, 2004). 

A step common to most optical sensing processes is the absorption of a photon. The quantitative relationship between the concentration of the absorber C and the attenuation of intensity of incident light is known as the Lambert-Beer law. For its derivation, it is convenient to invoke the particulate character of light, which says... 

Modern atomic theory received a shot in the arm when it was recognized that the individual atom has light absorption and emission spectra occurring at narrow lines of the spectrum at specific wavelengths, as opposed to the broad bands typical of the polyatomic molecules and compounds. Since the line spectrum of each element is characteristic of that element, atomic spectroscopy can be used for precise elementary analysis of many types of chemically simple and complex materials. These studies make use of the wave character of light, as well as light s particle character. 

COSMOS Occ. Sigil derived by WEI.LING 1735 to symbolise the complete universal character of light and darkness working together ... 

Each line in the line spectra can be considered as monochromatic radiation. Because of the wave character of light, each line in the spectrum is characterized in terms of its wavelength (A) ... 

Einstein insisted on the particle character of light. In the long wavelength limit of radio waves and alternating currents, the wave interpretation seemed to be the only possibility thongh. Concerning other types of EM radiation, it is easy to accept that y-rays are particles like a and p particles. In 1923, the American physicist Arthur Compton showed experimentally that electrons are scattered by x-rays. This experiment is very easy to interpret, if it is assumed that x-rays consist of particles. An interpretation in terms of waves is, in fact, also possible, but it had to wait for several decades. It was now concluded that Einstein was right in his proposal that x-rays consist of particles. Photon was accepted as a name for this elementary particle. 

In simple equipment, only relatively wide transmission bands are selected by means of colored glass or interference filters. A working beam of narrow bandwidth is obtained by combining this with a mercury source. Interference filters give spectral bandwidths in the 3-10-nm range [42], [68]. These operate on the principle of multiple reflections between layers of dielectric material that have been produced in a definite sequence by vacuum deposition. The wave character of light leads to interference of the reflected beams at... 

Louis Victor de Broglie (1892-) extended the dual character of light (wave and corpuscular) to matter. In 1924 he proposed that an electron in motion (as in a Bohr orbit) had a wave associated with it. C. J. Davisson, L. H. Germer, and G. P. Thomson found experimental evidence for this wave nature of particles in 1927 (Holum 1969, p. 37). 

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