I am trying to understand why light undergoes a phase shift when reflecting off one side of a half-silvered mirror, but not the other side.
- According to the Fresnel equations, a wave:
- Undergoes a phase shift of π when reflecting off the boundary with a denser medium.
- Does not undergo any phase shift when reflecting off the boundary with a less dense medium.
- When light approaches the silvered side of a half-silvered mirror and reflects off the air-to-glass boundary, it will undergo a phase shift (because glass is more optically dense than air).
- When light approaches the non-silvered side of a half-silvered mirror, enters the glass and then reflects off the glass-to-air boundary, it will not undergo a phase shift (because air is less optically dense than glass).
However, this explanation seems to completely neglect the silver coating. It seems to me that there is no air-glass boundary at all, but instead an air-silver boundary and a silver-glass boundary.
What am I missing?