Reflection, refraction and diffraction

If it is no longer possible to differentiate between the phenomena of specular reflection, refraction and diffraction because the diameter d of the sample to be assayed is disproportionately greater than the wavelength X of the light (i.e. the electromagnetic radiation), the reflection must be considered to be diffuse. 

Scattering. If the particles are small, which means of the order of the wavelength of light (about 0.5 pm) or smaller, the scattering of light can no longer be separated into reflection, refraction, and diffraction. If the size... 

The diffraction of light waves in such a film can be treated in the same way used by Rayleigh, that is, applying (macroscopic) Maxwell equations with the appropriate boundary conditions at both surfaces. Afterward it was found that the same answers are obtained when the interference of the reflected, refracted, and diffracted waves are treated in an elementary fashion by adding the diffraction of the single surfaces with appropriate phase factors. 

Particles for which a 1 fall into the so-called geometric scattering regime. In this case the scattering can be determined on the basis of the geometrical optics of reflection, refraction, and diffraction. Scattering is strongly dependent on particle shape and orientation... 

If ( ) denotes the geometric optics part and PjY( ) the diffraction part, the total phase function including reflection/refraction and diffraction processes is given by... 

On powdered samples, however, the effects of reflection, refraction and diffraction, summarized into scattering, cause severe losses in transmittance. According to theory [26], the scattered intensity Ij from an incident beam with Iq depends on the wavelength A, the volume V and the number of particles per volume unit N and the relative refractive index n, derived for spherical particles is... 

The overall result is that white light is returned from the film to the eyes of the observer, who concludes that the film is white. The greater the difference in refractive indices and the larger the number of particles up to a limiting concentration, the more milky and less transparent the film will appear. Transparent materials can appear white in powder form, because white light is reflected, refracted and diffracted at the many solid-air interfaces. 

Reflection, Refraction, and Diffraction Very Low Frequency (VLF), Low Frequency (LF), and Medium Frequency (MF)... 

Diffuse reflection (DR) spectra result from the radiation incident on a powdered sample that is absorbed as it refracts through each particle and is scattered by the combined process of reflection, refraction, and diffraction. That fraction of the incident radiation that reemerges from the upper surface of the sample is said to be diffusely reflected. Because DR spectra result from an absorption process, they have the appearance of transmission spectra (i.e., bands appear in absorption), unlike the case for Fresnel reflection spectra of bulk samples (see Chapter 13). When DR spectra are acquired on Fourier transform spectrometers, the singlebeam spectra of the sample and a nonabsorbing reference are measured separately and ratioed to produce the reflectance spectrum, Rfy). 

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