Main Question or Discussion Point
The atoms in a metal (ex. Cu) are arranged as a 3-D grating. But to our common sense ,smooth metal surfaces only reflect lights. Why can't we see diffraction from metal surfaces?
What do you mean for "imaginary part of n is responsible for absorption and reflection of EM waves" ?The metals contain a see of free electrons. In EM we know refractive index for metals is complex. Imaginary part of n is responsible for absorption and reflection of EM waves.