Hi all When one measures the reflectance of say silicon, certain peaks appear in the graph. I am wondering, if anyone can explain the location of the peaks and their meaning. Here the graph is, I hope the picture thing works, else here is the link. Spoiler The graph is for a polished silicon wafer. So I have a few ideas, which could make sense in my head: 1: It is related to the band gap with respect to the transmission spectrum, however, the band gap of silicon is 1.1 eV, which is why I am confused. I still think it could be related to the band gap, so now I am thinking, it is because the band gap may have other "paths", where it can conduct a current, but that it needs even more energy, to conduct through those gaps. But then I am confused, as the transmission is lowered at these areas.. 2: It is related to the imaginary part of the refractive index, which is very high at the <500 nm wavelength. So why does the reflectance peak, when the imaginary refractive index is high? I could understand it, as it relates to the extinction coefficient perhaps? A higher imaginary part would make a smaller penetration depth, and thus lower the transmission? But then why does it peak? Anyway thanks for helping and merry x-mas!