Why does light slow down in a medium such as glass, and does this imply that the photons leaving a lens are not the ones which entered?

In a submitted video, Dr. Don Lincoln asserts that re-emitted photons would go in random directions. However, in the generation of a laser beam, an incoming photon stimulates an excited atom to emit another photon. The emitted photon is in phase with, and moves in the same direction as, the incoming photon. In glass, each of these could go on to excite other molecules or stimulate other emissions.

Light slows down in transparent media like air, water and glass because the atoms and molecule absorb and reflect the photons and the strong and weak nuclear forces of those molecules and atoms slow down the speed and changes the wavelengths and frequencies of the photons. Some minerals have THREE indexes of refraction. No, the photons that go in are not the same photons that come out

This is my guess work. These are absorbed and re emitted. Frequency will not change but frequency will change.

You are running along a nice bitumen path. The path suddenly ends in soft dry sand. After some distance the path returns.

Do you slow down when you reach the sand?

Why? What makes you run slower on the sand?

Are you the same person when you leave the sand?

This is not a perfect analogy because you are using energy and the light is not.

However it is an example of how changing the medium ( sand) alters the behaviour but not the properties of an object ( you are still you. It is only the speed that changes).

In a medium the electric and magnetic forces increase for the same rate of change.

Therefore the rate of change ( and hence the speed) diminishes to balance.

When you leave the medium the electric and magnetic forces return to the previous value for the same rate of change ( a property of the medium ) so the transmission speed is restored to its previous value.

https://youtu.be/CUjt36SD3h8

I put the question to you , ; 'Why does light slowdown/stop in a medium such as a brick wall?'

Light does not pass through a brick wall!!! because the photons are reflected back at random angles.

Similarly light does slow down through a glass medium , because the some of the photons are 'bouncing off'' atoms in the glass, but other photons are passing throuhg (transparency).

Similarly the photons are slowed down through the medium of air.

The speed of light (c) which is the speed of photons is approx. 3,8 x 10^8 m/s and this is in a vacuum.

light slows down in those mediums because its index of refraction is greater than 1 in those mediums. there are molecules that impede light traveling, the photons are still the same as those that entered