From link:
Photon always travel at light speed "c" from the moment of its creation, therefore, it doesn’t have acceleration. A light signal bouncing between the two plates / mirrors in the light clock.
Thus how does a photon (either in particle or waveform) maintain its speed “c” again in the light clock after REFLECTION from the aforesaid mirrors repeatedly, Similarly, time still needed from its absorption to re-emission or using an auto-sensor to generate a new one?
I’m not exactly an expert on all this, but I’ll try. Firstly quantum physics is weird as all hell. Relativity is pretty weird too. Neither are very intuitive.
It seems like you are thinking of photon “particles” almost like tiny solid objects and trying to apply logic from everyday experience to what happens on a quantum level.
This appears to be quite common, and maybe largely due to illustrations always showing photons, electrons, etc. as little balls. But remember the illustrations are very vague representations. They have to draw something on the diagrams after all. But how do you properly draw some kind of wave-particle-energy-probability-WTF thing?
So, unless I misunderstood the question, you seem to think a photon should lose some velocity on reflection, much like a ball bouncing off a wall does?
It doesn’t. There is some loss in light intensity when you average out lots of photons, but each individual photon is either reflected with no loss of energy or absorbed (and possibly re emitted).
Photons are massless and travel at full speed always, regardless of reference frame.