Transmission multiple internal

Solid state spectra can be measured by the Attenuated Total Reflectance or Multiple Internal Reflection methods as well as by simple transmission techniques (222). Brooker (223) has reported the discovery of the translational vibrations of NaN02, NaNOs, and CaCOs (calcite). The orientation of the bonds in (U02)(N0s)2. 6 H2O has been ascertained from the spectra obtained in this manner (223). 

The sample absorbs the evanescent field so that the totally reflected wave is attenuated accordingly the reflectance spectrum closely resembles a transmission spectrum. Usually such spectra can actually be inteipreted and evaluated as transmittance, and commercially available accessories are designed to support this. With angles of reflection well above the critical one, some sensitivity is lost which however is regained by multiple internal reflections. How pronounced the actual spectrum is, can be adjusted by the number of reflections used, i.e. the sample-coated area of the slab whether both surfaces, one surface, or just a fraction. In any case the area of a given reflection should fully be covered to avoid spectral dilution. 

Infrared spectra can also be obtained by reflecting the IR beam on the surface of a sample. This technique is applied when it is not possible to obtain an IR spectrum by a transmission technique. Attenuated total reflectance (ATR) also known as ATIR (attenuated total internal reflectance) is based on multiple internal reflectance of the IR beam on the sample surface using a high refractive index crystal (e.g.. 

Hermann et al. (1969) have reviewed the subject of infrared spectroscopy at subambient temperatures, including an extensive literature review with over 6(X) references and discussions of work on pure molecules, and on molecules and molecular fragments within matrices. Hermann and coworkers (Hermann and Harvey, 1969 Hermann et al., 1969 Hermann, 1969) have also discussed the design of cells for use at low temperatures. These cells belong in four categories conventional transmission cells matrix isolation cells pseudomatrix isolation cells and multiple internal reflection cells (ATR). 

IR transmission of the Si-bonded wafers at a grazing angle of is a highly sensitive technique and does not require multiple internal reflections (which would necessitate a beveled Si substrate). The resulting spectra are the best for... 

Hydrophobic and hydrophilic bonded silicon wafers were studied by the methods of multiple internal reflection spectroscopy (MIR) and multiple internal transmission spectroscopy (MIT) [79, 81, 83, 84]. The sensitivity of the MIT configmation is 20-40 times higher than that of the traditional MIR configuration [81]. However, both of these techniques require beveled Si wafers. 

Good results in the IR spectroscopy of aqueous samples are given by the ATR technique (attenuated total reflection) and a further development of this, the MIR technique (multiple internal reflection) a prerequisite is that the sample space of the IR spectrophotometer is sufficiently large to accommodate the supplementary MIR device. The MIR technique likewise involves measurement of the absorption spectrum of the substance. All of the same molecule-specific and analytical conclusions can therefore be drawn as with an IR spectrum in the transmission of the same substance, even though the two spectra are physically not quite identical. 

Figure 11 Light path of the IR beam within a bonded silicon wafer pair used in the multiple internal transmission method. The IR radiation is totally reflected at the outer Si/air surfaces and tunnels repeatedly through the bonding interface.

A study of the feasibility of using infrared methods was conducted by the American Oil Company. Their results indicated that infrared studies of electrode surfaces by transmission or direct-reflection methods appear less promising than the internal-reflection technique. Even under favorable conditions, multiple internal-reflection studies (using germanium and silicon) proved... 

Internal reflection spectroscopy, also known as attenuated total reflectance (ATR) or multiple internal reflectance (MIR), is a versatile, nondestructive technique for obtaining the infrared spectrum of the surface of a material or the spectrum of materials either too thick or too strongly absorbing to be analyzed by standard transmission spectroscopy. 

A contemporary ventricular defibrillator lead consists of multiple internally separated metal wires that are externally encased in silicone rubber or polyurethane insulation. This allows the lead to function similarly to a standard pacemaker lead, i.e. transmission of electrical pacing/sensing signals between the heart and generator, but also structurally provides a separate pathway that participates in the delivery of shocks. This pathway includes what are commonly referred to as the lead "coil(s)." Shocks are delivered across the heart between the coil(s) and potentially the ICD can. Each element of the lead has its own pin that may connect to the ICD header. 

Figure 4.2 Schematic diagrams of some reflection spectroscopy techniques (a)-(c), internal reflection spectroscopy (a) and (b), single-reflection ATR (c), multiple internal reflection (MIR) (d) transflectance . Notes (i) collimated beam with ATR hemicylinder (ii) the component of specular reflectance (dotted line) will be superimposed on the double-pass transmission spectrum of the film in the transflectance measurement.

If the sample has a smooth, planar surface so that good physical contact with an infrared-transparent, higher refractive index prism/plate may be achieved, it can be examined by an infrared reflection technique, for example, one using attenuated total reflection, multiple internal reflection. It should be borne in mind, when examining polymeric films, that the sample may be a laminate and hence examination may give very different spectra from reflection at the two surfaces and also from transmission techniques. A coating or paint may be directly applied to a transparent plate for transmission or reflection techniques. 

Transmission spectroscopy is observed at a 90° angle (normal) of incidence. Reflectance spectroscopy, including specular, external (both single and multiple), internal (both single and multiple), and diffuse, is observed at smaller angles. 

A hollow waveguide (HWG) is essentially a hollow tube that transports light from one end to the other either by multiple mirror reflection or by total internal reflection. The hollow structure gives them several advantages (i) a high power threshold, (ii) low insertion losses, (iii) no end reflections, (iv) a small beam divergence, (v) robustness and - especially important for sensor applications - (vi) a wide spectral transmission range. 

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