Mirrors total external reflection

In order to calculate A.I/ I) from the measured PM IRRAS spectra, one has to determine functions J2 and Jq in an independent experiment. A reliable method to measure the PEM response functions was described by Buffeteau et al. [69]. Below we describe a similar method that we adapted with minor changes to use for electrochemical systems [81]. The spectroelectrochemical cell is replaced by the dielectric total external reflection mirror (a Cap2 equilateral prism can be used for this purpose). The second polarizer is inserted just after the PEM and set to admit p-polarized light (identical setting to that of the first polarizer). The PEM is turned off and the reference spectrum is acquired. This spectrum gives the intensity of the p-polarized light Ip (cal), which passes through the whole optical bench. 

Also, special Mossbauer spectrometers are used for total external reflection (TER) studies. On reflection at angles less than y j. the electromagnetic field intensity falls off rapidly (for the metal iron mirror, 3.8 X 10 sr). The penetration depth for the radiation (i.e. the thickness L of a layer under study) is taken to be equal to the depth at which the intensity is less by times e. If only the elastic scattering by electrons is considered, L is evaluated to be 1.3 nm for an iron mirror. 

Total external reflection occurs at angles 0 < 0, where the critical angle 9 .=(28)i 2 jg approximately inversely proportional to the X-ray energy, as shown in Figure 5. This allows the experimenter to eliminate harmonics by selecting an angle so that the fundamental is reflected from the mirror, but the harmonics are not. 

Under total external reflection condition, for 0 — 0, a standing-wave node lies at the mirror surface with the first antinode infinitely far above the surface. As the incident angle 9 is increased through the reflection, the first antinode moves inward until it coincides with the mirror surface for 9 = 9c. Above 9c, the first antinode remains at the mirror surface while the amplitude of the standing wave decreases very rapidly because of the drastic reduction in intensity of the specularly reflected plane wave. 

A majority of traditional NIR measurements are made on solid materials and these involve reflectance measurements, notably via diffuse reflectance. Likewise, in the mid-IR not all spectral measurements involve the transmission of radiation. Such measurements include internal reflectance (also known as attenuated total reflectance, ATR), external reflectance (front surface, mirror -style or specular reflectance), bulk diffuse reflectance (less common in the mid-IR compared to NIR), and photoacoustic determinations. Photoacoustic detection has been applied to trace-level gas measurements and commercial instruments are available based on this mode of detection. It is important to note that the photoacoustic spectrum is a direct measurement of infrared absorption. While most infrared spectra are either directly or indirectly correlated... 

In addition to being good diffracting structures, LSMs possess surfaces of mirror quality, making them excellent x-ray reflectors as well. Therefore, they can also be used as substrates for generating total external or specular reflection XSWs. 

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