(a) The reflectivity of metastable neon and helium from the same ridged grating surface which period is 5 \(\mu\)m and strip width is 100 nm as a function of the parameter \(\beta\). The solid line is the reflectivity calculated from [ref]. Dashed line is the numerical result of [ref]. Dash-dotted line is empirical result obtained by assuming an equivalent medium with effective absorption rate \(\frac{\nu}{d}\) [ref]. This image is from [ref] (b) The reflection and diffraction efficiencies \(S_m\) as a function of the parameter \(p\) (\(=\sqrt{\pi}\beta\)) up to 2nd diffraction order. Digits(circles) show the numerical results(total efficiency of scattering summing upto 8th order). This image is taken from [ref]