In the first, the ridges are along the x-direction (perpendicular to the aperture) and in the second, the ridges are along the y-direction in the second (parallel to the aperture). The two orientations are shown in Figure . We filled each channel with water and scanned the ASMAA aperture along the x-direction. As observed in Figure , the difference in ATR ridge orientation has a significant impact on both the light intensity and the water absorbance profiles when coupled with the scanning aperture. In the first case when the ridges are positioned along the x-direction, an x-scan of the moving aperture produced a continuous change in intensity, which peaked near the centre of the device and tailed off slightly at the edges with an approximately Gaussian profile (Figure ). In the case when the ATR ridges were oriented along the y-direction, a series of oscillations in the intensity and absorbance values were observed as a function of the aperture displacement, which were enveloped with a similar Gaussian profile (Figure ). Moreover, we drop a water on top of crystal, and repeat x-scan twice with ATR ridges oriented along the x-and y-direction, successively. By integrating the peak at 3300 cm -1 of each spectrum, we obtained 2 cross-section plot profile curves which exhibited the same shape (Figure ). The latter behaviour was observed previously using an aperture scanning approach in the same orientation and as well using a scanning synchrotron beam and is related to light lost to refracted light being split into divergent paths, which are then blocked by the aperture plate on their way out. In this case, aligning channels along the ridges, can take advantage of peaks in light throughput, could be advantageous.