  Atmospheric air Cherenkov telescopes are successfully used for ground-based,
very high-energy (VHE) gamma ray astronomy. Triggers from the so-called single
muon and other long-flying relativistic charged particle events are an unwanted
background for the Cherenkov telescope. Because of low rate at TeV energies the
muon background is unimportant. It is much more intense for telescopes with
high photon sensitivity and low energy threshold. Below a few hundred GeV
energy, the so-called muon background becomes so intense, that it can
deteriorate the sensitivity of telescopes (the so-called muon-wall problem).
  From general considerations it can be anticipated that the signature of these
particles should be a light pulse with a narrow time structure. In fact,
simulations show that the pulses from muons have a very narrow time profile
that is well below the time resolutions of nearly all currently operating
telescopes. In this report we elaborate on the time profile of Cherenkov light
from the so-called single muons and show that a telescope with ultra-fast time
response can open a new dimension allowing one to tag and to reject those
events.
