Read me file: Xu Fang, School of Electronics and Computer Science, University of Southampton, x.fang@soton.ac.uk . The excel file contains all the data for the paper: Fei He, Kevin MacDonald & Xu Fang, Coherent illumination spectroscopy of nanostructures and thin films on thick substrates, Optics Express. The paper has 5 figures in total, from Figure 1 to Figure 5. Only Figures 2(b), 3(b), 4(a), 4(b) and 5 have data: Figure 2(b): Spectral dispersion of metasurface absorption. Figure 3(b): Spectral dispersion of metasurface absorption. Figure 4(a): Spectral dispersion of absorption for a 2 nm SiO2 layer on a semi-infinite Si substrate. Figure 4(b): Magnitude of coherent absorption at a wavelength of 9.3 µm. Figure 5: Evaluating SiO2-on-Si layer thickness via coherent absorption modulation. Date of data collection: from Oct 2017 - Jan 2018. Information about geographic location of data collection: University of Southampton, U.K. Date that the file was created: Apr 2018.