Reflections, reducing with surface coatings

ATR studies of the biocorrosion of submerged copper surfaces have been reported. The IRE of a cylindrical internal reflectance cell (CIRCLE) was coated with a thin copper layer via a vacuum deposition technique (105). The copper layer reduces the sampling depth of the radiation outward from the surface of the IRE. Therefore, the intensity of the water bending band will vary with copper layer thicknesses of 4.1 nm or less. The copper layers were shown to be stable to exposure to water alone, but the presence of acidic polysaccahrides in the water caused a reduction in the copper layer thicknesses (106.107). The adsorption of a model compound, Gum Arabic, onto the coated IRE was detected by increases in the C-O stretching band of the pyranose units near 1050 cm"1 (106). 

The AR coating can provide transmission enhancements by reducing secondary surface reflections at glass interfaces. This improvement can be realized by up to a 7% increase in filter throughput (3). AR coatings on emission filters and dichroic mirrors also reduce the ghost image sometimes seen in optical pathways with multiple reflective surfaces. 

To reduce the specular reflectance collected by an on-axis accessory, different mechanical devices are used. One example is the patented Blocker, which represents a small gold-coated blade [152]. When placed across the sample surface so as to bisect it (Fig. 4.29), the Fresnel specular component is blocked from the collection mirror, and only the IR radiation penetrating into the powder reaches it. It should be taken into account that the Blocker can reduce radiation reflected from rough surfaces by 85% [152] or even more [153]. On the other hand, the Blocker is effective not only with powders but also with rough (textured) surfaces and was shown [153] to reduce the Fresnel diffuse component, along with the specular one. 

Metallic pigments reflect infrared radiation and hence are able to reduce the heat emission from a surface coated therewith, according to Kirchhoff s law 1-/J(A.) = e(X,), where R = reflectance and e = emissivity. Hybrid polymers are superior to commercially available binders, considering both miscibility with IR-reflective pigments and the achievable degree of filling. However, in order not to affect the optical function of the pigments, the infrared absorption of the binder should also be as... 

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