Total Internal Reflection

In total internal reflection of light for example, at a glass-air interface or from a water-air surface if the incident light is in the more dense medium, does the light penetrate into the air beyond the interface?

Answer

Yes, the light goes a little beyond the interface. One can treat this behavior either classically or quantum mechanically. In QM the wave function for the photon extends beyond the glass air interface into the air.

You can see this behavior in the following manner. Fill a drinking glass partially full with water. Tilt the glass and look down into it at the side wall at such an angle that the light entering your eye has been totally internally reflected from the wall. The wall will look silvery when this condition holds. Then press your moistened thumb against the outside of the glass. You will see the ridges of your fingerprint because, at those points, you will have interfered with the total reflection process. The valleys between the ridges are still far enough away from the glass that the reflection here remains total and you simply see a silvery whorl.