Immersion medium

Procedure Water was taken as an immersion medium. The object under study was placed on a wet specimen stage so that the section of its surface to be investigated should be above the scanning zone and was clamped by a slide. After that OCM images of the biological object were acquired. The images were recorded and stored in the personal computer for further analysis. 

Fresnel Refection losses—Reflection losses that are incurred at the input and output of optical fibers due to the differences in refraction index between the core glass and immersion medium. 

Figure 15.22 shows the long-term effect of a heat cured one-part epoxy adhesive to various chemical environments. As can be seen, the temperature of the immersion medium is a significant factor in the aging properties of the adhesive. As the temperature increases, the adhesive generally adsorbs more fluid, and the degradation rate increases. 

If the immersion medium is strongly alkaline, the anions will remain in solution, but if it is weakly alkaline or neutral, dissociation of a polysulfide will occur as it departs the concrete, and sulfur will precipitate either on the concrete surface or in the surrounding liquid. In either case the concrete should be leached of sulfur, but the process is much slower with neutral media, possibly because diffusion of leachate and polysulfide is slowed as sulfur precipitates near the surface. 

The inherent instability of sulfur-infiltrated concrete in aqueous media illustrated in this study may be the most important factor in utilization, because it will affect long-term durability of the concrete in many natural settings. The Ca(OH)2 produced by the hydration of portland cement is a principal reactant in the leaching process, and while it remains sulfur could be extracted, leaving the matrix vulnerable to other destructive processes. The removal rate of sulfur will vary greatly, depending mostly upon the pH of the immersion medium thus, the concrete deteriorates in alkaline sulfatic soils but is relatively stable in the corrosive neutral sulfatic solutions from the sodium sulfate plant. 

To quantify the results a combination of the signal amplitude of the interfacial echo (IE) in a C-scan, expressed through a colour code, and the adhesion strength obtained destructively by an ASTM C633-13 (2013) tensile test can be used. Echo-impulse techniques with an auxiliary reflector, for example by using water as an immersion medium allow measuring reliably the adhesion of very thin coatings... 

Fig. 3. The one-to-one mapping between A and i/> and n and k. Dielectrics, having k = 0, are located on the basal diameter. "Perfect (high conductivity) metals are located near the periphery. This diagram is for = 70° refractive index of the immersion medium = 1.

Fig. 4. The "ideal three-phase model. Medium 1 is the immersion medium, medium 2 is a parallel-sided film of homogeneous, isotropic properties, and medium 3 is the perfectly plane, smooth substrate.

Fig. 29. Double refraction of collagen fibers produced by fibroblast cultures of chick embryo explants, after Pfeiffer (172). Retardation, r, in m/t is plotted, as ordinate, against the refractive index, n, of the immersion medium. Curve A is for fibers fixed in Helly s fluid (containing formalin), and curve B shows the result of fixation in tannic acid.

Condition the samples as specified, and carry out (he test as quickly as possible after removal from the conditioning atmo,sphere. Allow bubbles to disperse if the test is to be in a liquid immersion medium. 

The degree of deviation of the thin-film approximation from the exact spectral simulations depends upon the refractive indices of the immersion medium and the substrate 113, the oscillator strength of the film, and on the angle of incidence (Pi. The deviation can be more than 10% for a 50-nm film and several percent for a 1-nm film (Sections 2.2, 2.5, 3.3, and 3.10). 

The angular dependences of the MSEFs in a film at the air-Al and water-Al interfaces shown in Fig. 1.17a are remarkable in three respects. First, independently of the immersion medium, the z-component of the electric field within the film is dominant, while the x- and y-components are almost zero at aU angles of incidence (p. In other words, the tangential electric fields are quenched. This is observed for all metals. The second feature, which is common to all substrates in air (e.g., compare with Fig. 1.15a), is the attenuation of the perpendicular MSEF component, whose maximum value for Al is 0.73. It can be shown [161] that such an attenuation of the (El)-component in the case of a metal substrate is observed for films with 2 > 1-4, which includes the majority of films. Finally, it should be noted that if the radiation is incident fi om water onto a metal substrate, the perpendicular MSEFs within the film are enhanced by a factor of about 2, as for Si substrates (Fig. 1.15a). 

Figure 2.1. Optical schemes for recording oblique-incidence transmission spectra of nanolayers, in which layer is located (a, b) on surface of hemicylinder, (c) on surface of plane-parallel plate, (d) between two hemicylinders (1) immersion medium with refractive index ni, (2) layer under investigation of thickness d2 and with optical constants 02 and kz, (3) transparent substrate with refractive index n%.

Thus, in the case of weakly reflecting metal snbstrates, the maximnm intensity of the IRRAS spectmm can be achieved with one reflection, whereas in the case of strongly reflecting metals, the optimum number of reflections, Aopt, should be calculated with Eqs. (2.2) or (2.3), depending on the type of spectrometer used. The optimum angles of incidence are 80-85° and 75°-80°, respectively, for single and multiple reflection. In addition, surface sensitivity of the method can essentially be enhanced by nsing the immersion medium technique (Section 2.5.2). 

Figure 2.32. Experimental spectra of AI2O3 layer on Al mirror heated at t = 550°C in air for 0.5 h, using p-polarized IRRAS at = 60° (1) sample in air, (2) sample in contact with immersion medium (KRS-5). Reprinted, by permission, from V. P. Tolstoy and S. N. Gruzinov, Opt. Spectrosc. 63, 489-491 (1987), p. 490, Fig. 4. Copyright 1988 Optical Society of America.

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