  In this paper,we have investigated three external fields interacting with the
four-level atomic system described by the density-matrix approach.The atomic
system exhibits left-handedness with zero absorption as well as large negative
refractive index.Varying the parameters of the three external fields,the
properties of zero absorption,large negative refractive index from the atomic
system keep unvarying.Our scheme proposes an approach to obtain negative
refractive medium with zero absorption. The zero absorption property of atomic
system may be used to amplify the evanescent waves that have been lost in the
imaging by traditional lenses.And a slab fabricated by the left-handed atomic
system may be an ideal candidate for designing perfect lenses.
