Optical wave, attenuation

Shock wave velocity in an inert material as a function of the distance from the explosive charge/inert material interface is determined on the basis of view ing a laser beam that is reflected from the optical barriers in the inert material by a photomultiplier and an oscilloscope. From the plot of the shock wave velocity vs. distance (shock wave attenuation curve) obtained for an inert... 

The imaginary part gives a (hnear) attenuation factor in the propagation of a plane optical wave exp( co/c)n(co)/, where / is the propagation length into the medium. The attenuation constant (co/c)n is usually referred to as the linear absorption constant in units of (length). o( ) is the dispersion of the medium (see Fig. 10.6a). n (co) gives the hnear absorption spectral line shape which is a Lorentzian (see Fig. 10.6b). 

Up to this point, we have calculated the linear response of the medium, a polarization oscillating at the frequency m of the applied field. This polarization produces its own radiation field that interferes with the applied optical field. Two familiar effects result a change in tlie speed of the light wave and its attenuation as it propagates. These properties may be related directly to the linear susceptibility The index of... 

There was thus the need for optical experiments showing the flaws of classical electrodynamics. An important difference between a wave and a particle is with respect to a beam splitter a wave can be split in two while a photon can not. An intensity correlation measurement between the two output ports of the beamsplitter is a good test as a wave would give a non zero correlation while a particle would show no correlation, the particle going either in one arm or the other. However, when one takes an attenuated source, such as the one used by Taylor, it contains single photon pulses but also a (small) fraction of two... 

To increase the speed of the TIRF-based kinetic techniques, the perturbation can be optical rather than chemical. If the evanescent wave intensity is briefly flashed brightly, then some of the fluorophores associated with the surface will be photobleached. Subsequent exchange with unbleached dissolved fluorophores in equilibrium with the surface will lead to a recovery of fluorescence, excited by a continuous but much attenuated evanescent wave. The time course of this recovery is a measure of the desorption kinetic rate k2. This technique1-115) is called TIR/FRAP (or TIR/FPR) in reference to fluorescence recovery after photobleaching (or fluorescence photobleaching recovery). 

A fiber-optic device has been described that can monitor chlorinated hydrocarbons in water (Gobel et al. 1994). The sensor is based on the diffusion of chlorinated hydrocarbons into a polymeric layer surrounding a silver halide optical fiber through which is passed broad-band mid-infrared radiation. The chlorinated compounds concentrated in the polymer absorb some of the radiation that escapes the liber (evanescent wave) this technique is a variant of attenuated total reflection (ATR) spectroscopy. A LOD for chloroform was stated to be 5 mg/L (5 ppm). This sensor does not have a high degree of selectivity for chloroform over other chlorinated aliphatic hydrocarbons, but appears to be useful for continuous monitoring purposes. 

Attenuated total reflectance infrared (ATR-IR) is used to study films, coatings, threads, powders, interfaces, and solutions. (It also serves as the basis for much of the communication systems based on fiber optics.) ATR occurs when radiation enters from a more-dense material (i.e., a material with a higher refractive index) into a material that is less dense (i.e., with a lower refractive index). The fraction of the incident radiation reflected increases when the angle of incidence increases. The incident radiation is reflected at the interface when the angle of incidence is greater than the critical angle. The radiation penetrates a short depth into the interface before complete reflection occurs. This penetration is called the evanescent wave. Its intensity is reduced by the sample which absorbs. 

In internal reflection spectroscopy (IRS) the sample is in optical contact with another material (e.g. a prism). The prism is optically denser than the sample. The incoming light forms a standing wave pattern at the interface within the dense prism medium, whereas in the rare medium the amplitude of the electric field falls off exponentially with the distance from the phase boundary. If the rare medium exhibits absorption, the penetrating wave becomes attenuated, so the reflectance can be written... 

Optics und hence guided wave velocity can be controlled with great precision acceptable attenuation loss. Possible uses in conventional optics and optical data storage, pboiochromic and ablative systems. Optical sensors e g. based on coated fibres. 

Looking at the phenomenon of optical absorption by the medium from the viewpoint of classical wave mechanics, we see that the attenuation of electromagnetic radiation can be attributed to the interaction of the oscillating electric vector with the medium. Any phenomenon involving periodic oscillations can be decomposed to real and imaginary components. Thus, the ordinary refractive index n is the real part of the index of refraction n, which can be written as... 

Attenuated total internal reflection (ATR) probes offer several advantages over other probe types. ATR is a phenomenon that relies on a difference in the index of refraction of a crystal and that of the solution with which it is in contact to prevent light from escaping the crystal. Only the evanescent wave of the light interacts with the solution layer at the crystal face. The result is an optical pathlength of only a few microns. Typical designs make use of faceted crystals or hemispheres (see Figure 6.1). The most common ATR material in the UV-vis is sapphire. In rare cases, fused silica may be used. ATR allows spectra to be taken of neat samples with optical density (OD) of 500-1000... 

Atmospheric attenuation properties of millimeter waves can be important, especially in specific bands. Electromagnetic waves effectively pass through the atmosphere without significant losses over much of the spectmm, including many portions of the microwave, millimeter-wave, IR, and optical bands. However, significant absorption because of water vapor or other atmospheric constituents does occur over several narrow frequency bands in the millimeter-wave band and is extremely significant over much of the terahertz band. Atmospheric attenuation is covered in detail in Section 4.6. 

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