Electromagnetic radiation incident

Visible light or other electromagnetic radiation incident on a solid, liquid, or gas can liberate electric charges. This is called photoelectricity. Ejection of electrons from the surface is usually called photoemission. Electrons or positive ions formed in a gas as the result of such radiation is called photoionization. Such a process, however, cannot charge a particle directly. The charging process in that case is a direct result of subsequent diffusion. 

The attenuation of electromagnetic radiation as it passes through a sample is described quantitatively by two separate, but related terms transmittance and absorbance. Transmittance is defined as the ratio of the electromagnetic radiation s power exiting the sample, to that incident on the sample from the source, Pq, (Figure 10.20a). 

Fig. 3—Measurement of surface by HDI surface reflectance analyzer. In electromagnetic radiation (light), the polarization direction is defined as the direction of the electric field vector. The incident polarization of the light can be controlled. The instrument uses a variety of detectors to analyze the reflected polarization state of the light. (U.S. Patent 6,134,011). (a) Plane of the disk The SRA uses a fixed 60 degree (from the surface normal) angle of incidence. The plane of incidence is the same as the paper plane (b) Pit on a surface detected by reflected light channels of HDI instrument (c) Scratches on disk surface measured by HDI surface reflectance analyzer (d) Particles on the surface of disk detected by reflected light (black spot) and by scattered light (white spot) [8].

The method by which incident radiation interacts with the medium to cause ionization may be direct or indirect. Electromagnetic radiations (x rays and gamma photons) are indirectly ionizing that is, they give up their energy in various interactions with cellular molecules, and the energy is then utilized to produce a... 

Specular reflection of electromagnetic radiation at the (electrochemical) interface is generally described by Fresnel equations. Supposing the most simple case that both the electrolyte and electrode are transparent and differ only in their refractive indexes, nx and n2, the reflectivity for normal incidence of the radiation equals ... 

As the frequency of the incident electromagnetic radiation approaches that of die transition n m, the first term in the brackets of Eq. (86) dominates it... 

The rapidly varying electric held of the incident electromagnetic radiation can, therefore, cause a rapid fluctuation in the dipole moment of the molecule. The magnitude of this oscillation depends on the polarisability of the molecule but is generally small. 

X-ray diffraction. The mechanism by which atoms diffract or scatter electromagnetic radiation via the coupling of the electron cloud of the atom to the incident oscillating electric field was discussed in the section on SERS. The X-rays scattered by an atom are the resultant of the waves... 

If a substance is irradiated with electromagnetic radiation, the energy of the incident photons may be transferred to the atoms or molecules raising them from the ground state to an excited state. This process, known as absorption, is accompanied by attenuation of the incident radiation at a particular frequency and can occur only when the energy difference between the two levels is exactly matched by the energy of the photons. The frequency of the radiation is given by... 

In addition to emitting electrons, a solid bombarded with ions in the keV range emits electromagnetic radiation from the near infrared to the near ultraviolet, with a photon yield of typically KT4 per incident ion for a metal, and 10 2 to 10 l for insulators. If the primary beam is intense, as in the dynamic SIMS range, and the sample is an insulator, one observes a bright glow at the point where the beam hits the sample. With conductors, the effect is not or hardly observable. 

The color of an object is a sensory impression received by the individual and triggered by a color stimulus. The color stimulus consists of light from the object incident on the eye, light denoting electromagnetic radiation in the range of wave-... 

Most of the four above-mentioned properties for Raman spectra can be explained by using a simple classical model. When the crystal is subjected to the oscillating electric field = fioc " of the incident electromagnetic radiation, it becomes polarized. In the linear approximation, the induced electric polarization in any specific direction is given by Pj = XjkEk, where Xjk is the susceptibility tensor. As for other physical properties of the crystal, the susceptibility becomes altered because the atoms in the solid are vibrating periodically around equilibrium positions. Thus, for a particular... 

The reflectivity of a solid can also be determined after establishing the boundary conditions for the electromagnetic radiation at the interface between the solid and the vacuum. In the simple case of a solid in a vacuum, and considering normal incidence of light, it is well known from basic optics texts that... 

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