Short Distance sensitive laser range finder
Your task screams "Please, use interferometer" here :-)
Basically, you measure phase difference between laser itself &amp; reflected beam through interference.

This way you may get precision down to 0.1 micron, but you should be ready to count all these 10'000 phase changes per second (I.e. if you skip one - you've got 0.7 micron error).

Speed of tracked object is virtually unlimited.

But this is not going to be weekend project :-)