  We develop a semiclassical theory to describe the photon momenta in
left-handed materials (LHMs). A single two-level atom is introduced as an
"explorer" to probe the momenta of photons. We demonstrate that the linear
momentum of the photons reverses its direction in LHMs. However the orbital
angular momentum is remains unreversed, although the wave-fronts reversed their
screwing fashion. We theoretically predict that the spin angular momentum is
also unreversed. The investigation of photon momenta will provide insights into
the fundamental properties of LHMs.
