We show how a collection of noninverted two-level systems, under the a
ction of a quasiresonant pump field, can produce an exponential amplif
ication of a probe signal through the mechanism of a dynamical instabi
lity with spatial seIf-bunching in a way very similar to that experien
ced by a high-gain free-electron laser. We offer a detailed descriptio
n of this phenomenon, specify the conditions under which it takes plac
e, and sketch possible experimental parameters for its observation in
a gaseous medium.