Will laser scanning system miss photons when the mirror scans too fast? So in many applications like Optical Coherence Tomography, LIDAR, a mechanical scanning mirror is often used to reflect the laser to outside and also reflect the back scattered light to detector.
Since light has a constant speed, when the light hits the mirror at scan angle A and goes out side, then gets back scattered by an object and goes back to the mirror, the mirror already moved to another angle. My understanding is that if the mirror scans extremely fast, or if the object is far far away, then the mirror will not be able to reflect the light back to the sensor.
On the other hand, assume I am going with the light, then time will freeze, in light's perspective, the mirror will be static between the two reflections, one going out, one going back to the detector.
I am sure I missed something here but could not figure out...
 A: From light's perspective, if it had one, it would see no distance or time, it would just arrive instantaneously. But since time is relative, it sees what you think of as the past and future as the same time. So in the lab frame, light can be sent from a source that misses an object if it doesn't make it there in time.
A: Photons are elementary particles, massless, they travel at speed c when measured locally in vacuum.
Now photons travel along lightlike worldlines, that is as long as the photon exists(between emission and absorption) it travels a spacetime distance of 0.
The emission and absorption are casually connected for the photon and these two events' spacetime distance is 0.
This is where you get confused.
Photons do not have a reference frame, you cannot say what it looks like from the photons view. In reality, you could say that the photon sees all this timescale between emission and absorption in one. It is because photons do not experience time as we do (who have rest mass).
Now from our frame (who have rest mass), this takes time, between emission and absorption, and in your case you can interact with the photon.
This interaction is called elastic scattering, this is what happens when a photon hits a mirror.
Now elastic scattering keeps the energy of the photon. Energy is conserved.
It changes its momentum (vector), and yes, the photon exerts pressure on the mirror.
Photons travel at speed c in vacuum, when measured locally. It travels at speed c, then it changes angle, and travels at speed c.
Photons do not slow down, and speed up. They just change angle. Momentum is conserved.
Now where you get confused is how can the mirror rotate while the photon travels back?
You say time will freeze. It does not freeze. It is just that for the photon in spacetime emission and absorption are not separate, but connected by casuality.
This does not mean that we cannot interact with the photon. In our frame, the space and time distance the photon travels can have interactions with the photon. And in this frame, the mirror rotates.
The photon does not have a frame, but if you want to say what the photon sees, you shouldn't say time freezes. It is rather that the photon sees the whole timescale in one.  That includes the rotation of the mirror, the elastic scattering. 
