Understanding Photon Slowdown and Acceleration in Material-Filled Space

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Delta2
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How do photons slowdown when they move from empty space to a space filled with some material, and how do they accelerate again to c when they move out of the material back to void? (i.e like when they pass through a piece of glass with emptyspace on both sides of it). Is there some kind of force exerted to the photon?
 

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The "slowdown" is due to the photon being absorbed and re-emitted. In between absorptions, the photons travel at c.
 
Matterwave said:
The "slowdown" is due to the photon being absorbed and re-emitted. In between absorptions, the photons travel at c.

This is incorrect, but that misconcepption is so common that these forums already have a FAQ entry on that: https://www.physicsforums.com/showthread.php?t=511177.

The mechanisms for slowing down light are sometimes interactions with common modes as described in the FAQ above. In many materials light induces a polarization in the material which in turn acts on the light field. The consequences are phase shifts which effectively result in slower light.