of the spectral response, the integrated reflection-absorption intensity, of these samples are slightly greater than the intensity of the spectral response of the same samples measured via a 60 ° angle of incidence data (Figure 3). This behavior is expected due to the increase in reflection-absorption sensitivity with increasing angle o f incidence. Here, too, the average initial slope (and hence instrument sen-sitivity) is the same for both transverse and longitudinal orientations. The pronounced non-linearity in slope for the thickest films at 75° angle-of-incidence was unexpected. A n increasingly non-linear response may be observed for thicker absorbing films, and this effect will become more pronounced as the angle of incidence is also increased. The interpretation of the data implying that measurement of a thicker film, sampled at a steeper angle, generated the observed non-linearity in the data is not substantiated by th e calculated spectra for the pre-sent measurement conditions due to the small change from 60 to 75° in the angle of incidence. Furthermore, such a non-linear effect would be most pronounced for measurements on the smoothest substrat e (Figure 4, filled circles) where the ef-fective local orientation of the surface is most constant with respect to the illumi-nation beam. Instead of observing such non-linear behavior the measurements made on the smoothest surface are by far the most linear sample series for the 75° data . We attribute the pronounced non-linearity of the 75° data for the thickest draw-ing-agent films to the morphological characteristics of the material as deposited o n the aluminum test panel surface. As described above, the drawing-agent mate-rial is highly viscous and forms a visibly heterogeneous white film at l-|im thick-ness. Variations in the deposition process produce relatively thick local areas of drawing-agent film and result in accretion of solid residue along the polishing grooves and ridges of the aluminum substrate. Under these circumstances, illumi-natio n of the surface with the FTIR beam at an angle of 75° may result in shadow-ing by contaminant material on ridge structures for all except the smoothest (600 grit polish) surface. The 12-mm diameter focal area of the infrared beam is elon-gated by a factor o f four for this angle of incidence. In contrast, reflectance meas-urements at 60° result in only a factor of 2 elongation, and minimize the shadow-ing effect of thick films except for ridges on the roughest (80 grit polish) surfaces. This interpretation is substantiated by reflectance data for the second test set (lubricant material) as shown in Figure 5. FTIR reflectance measurements have been made at 75° angle-of-incidence for a test series similar to that of the draw-ing-agent set. An analysis of the C-H stretching frequencies shows a strikingly more linear dependence of instrument response with film thickness (with the ex-ception of a single point for one of the panels with a 220 grit surface finish). We believe that this is due to the more fluid characteristic of the lubricant material, which allows the deposited film to conform much more closely to the surface to-pography of the test coupons. This behavior may also account for the stronger de-pendence of the integrated intensity slope with surface roughness, when compared to the nearly constant results for the drawing-agent contaminant examined above.

DOI link for of the spectral response, the integrated reflection-absorption intensity, of these samples are slightly greater than the intensity of the spectral response of the same samples measured via a 60 ° angle of incidence data (Figure 3). This behavior is expected due to the increase in reflection-absorption sensitivity with increasing angle o f incidence. Here, too, the average initial slope (and hence instrument sen-sitivity) is the same for both transverse and longitudinal orientations. The pronounced non-linearity in slope for the thickest films at 75° angle-of-incidence was unexpected. A n increasingly non-linear response may be observed for thicker absorbing films, and this effect will become more pronounced as the angle of incidence is also increased. The interpretation of the data implying that measurement of a thicker film, sampled at a steeper angle, generated the observed non-linearity in the data is not substantiated by th e calculated spectra for the pre-sent measurement conditions due to the small change from 60 to 75° in the angle of incidence. Furthermore, such a non-linear effect would be most pronounced for measurements on the smoothest substrat e (Figure 4, filled circles) where the ef-fective local orientation of the surface is most constant with respect to the illumi-nation beam. Instead of observing such non-linear behavior the measurements made on the smoothest surface are by far the most linear sample series for the 75° data . We attribute the pronounced non-linearity of the 75° data for the thickest draw-ing-agent films to the morphological characteristics of the material as deposited o n the aluminum test panel surface. As described above, the drawing-agent mate-rial is highly viscous and forms a visibly heterogeneous white film at l-|im thick-ness. Variations in the deposition process produce relatively thick local areas of drawing-agent film and result in accretion of solid residue along the polishing grooves and ridges of the aluminum substrate. Under these circumstances, illumi-natio n of the surface with the FTIR beam at an angle of 75° may result in shadow-ing by contaminant material on ridge structures for all except the smoothest (600 grit polish) surface. The 12-mm diameter focal area of the infrared beam is elon-gated by a factor o f four for this angle of incidence. In contrast, reflectance meas-urements at 60° result in only a factor of 2 elongation, and minimize the shadow-ing effect of thick films except for ridges on the roughest (80 grit polish) surfaces. This interpretation is substantiated by reflectance data for the second test set (lubricant material) as shown in Figure 5. FTIR reflectance measurements have been made at 75° angle-of-incidence for a test series similar to that of the draw-ing-agent set. An analysis of the C-H stretching frequencies shows a strikingly more linear dependence of instrument response with film thickness (with the ex-ception of a single point for one of the panels with a 220 grit surface finish). We believe that this is due to the more fluid characteristic of the lubricant material, which allows the deposited film to conform much more closely to the surface to-pography of the test coupons. This behavior may also account for the stronger de-pendence of the integrated intensity slope with surface roughness, when compared to the nearly constant results for the drawing-agent contaminant examined above.

of the spectral response, the integrated reflection-absorption intensity, of these samples are slightly greater than the intensity of the spectral response of the same samples measured via a 60 ° angle of incidence data (Figure 3). This behavior is expected due to the increase in reflection-absorption sensitivity with increasing angle o f incidence. Here, too, the average initial slope (and hence instrument sen-sitivity) is the same for both transverse and longitudinal orientations. The pronounced non-linearity in slope for the thickest films at 75° angle-of-incidence was unexpected. A n increasingly non-linear response may be observed for thicker absorbing films, and this effect will become more pronounced as the angle of incidence is also increased. The interpretation of the data implying that measurement of a thicker film, sampled at a steeper angle, generated the observed non-linearity in the data is not substantiated by th e calculated spectra for the pre-sent measurement conditions due to the small change from 60 to 75° in the angle of incidence. Furthermore, such a non-linear effect would be most pronounced for measurements on the smoothest substrat e (Figure 4, filled circles) where the ef-fective local orientation of the surface is most constant with respect to the illumi-nation beam. Instead of observing such non-linear behavior the measurements made on the smoothest surface are by far the most linear sample series for the 75° data . We attribute the pronounced non-linearity of the 75° data for the thickest draw-ing-agent films to the morphological characteristics of the material as deposited o n the aluminum test panel surface. As described above, the drawing-agent mate-rial is highly viscous and forms a visibly heterogeneous white film at l-|im thick-ness. Variations in the deposition process produce relatively thick local areas of drawing-agent film and result in accretion of solid residue along the polishing grooves and ridges of the aluminum substrate. Under these circumstances, illumi-natio n of the surface with the FTIR beam at an angle of 75° may result in shadow-ing by contaminant material on ridge structures for all except the smoothest (600 grit polish) surface. The 12-mm diameter focal area of the infrared beam is elon-gated by a factor o f four for this angle of incidence. In contrast, reflectance meas-urements at 60° result in only a factor of 2 elongation, and minimize the shadow-ing effect of thick films except for ridges on the roughest (80 grit polish) surfaces. This interpretation is substantiated by reflectance data for the second test set (lubricant material) as shown in Figure 5. FTIR reflectance measurements have been made at 75° angle-of-incidence for a test series similar to that of the draw-ing-agent set. An analysis of the C-H stretching frequencies shows a strikingly more linear dependence of instrument response with film thickness (with the ex-ception of a single point for one of the panels with a 220 grit surface finish). We believe that this is due to the more fluid characteristic of the lubricant material, which allows the deposited film to conform much more closely to the surface to-pography of the test coupons. This behavior may also account for the stronger de-pendence of the integrated intensity slope with surface roughness, when compared to the nearly constant results for the drawing-agent contaminant examined above.