Wednesday, June 5, 2019

optics - Does light change phase when reflecting off a metal surface?


If you shine monochromatic light on a reflective metal surface, say polished silver, does the reflected light undergo a $180^{\circ}$ phase change like it does when it reflects off a medium with a higher refractive index?




Answer



Yes, if the metal has infinite conductivity so the induced currents in it are in anti-phase with the electric field of the primary wave.


In practice, metals have finite conductivity, the oscillations of charges on the surface will be slightly off the anti-phase so the reflected wave will have phase shift lower than 180 degrees.


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