1. The problem statement, all variables and given/known data Hi This isn't homework, but something I've wondered about. I post it here, because it might be helpful to others. Say I am looking at the attached optical system: I have polarized light in the plane. Then it hits a lambda/4-plate, where the angle between the fast axis and the polarization of the light is denoted Ω. The light then gets reflected on a mirror, and moves through the quarter wave-plate again. If Ω=0 degrees, light will just go back the same way it came with the same polarization. If Ω=45 degree, light becomes circularly polarized after the wave-plate, changes rotation direction after the reflection and becomes linearly polarized again. In total a phase change of 360 degrees (180 from the reflection and 180 from passing through the waveplate twice). So this is the same as the case with Ω=0? This doesn't make sense to me. Can anyone point out where my reasoning is wrong? Best, Niles.