  We suggest a method to generate coherent short pulses by generating a
frequency comb using lasing without inversion in the transient regime. We use a
universal method to study the propagation of a pulse in various spectral
regions through an active medium that is strongly driven on a low-frequency
transition on a time scale shorter than the decoherence time. The results show
gain on the sidebands at different modes can be produced even if there is no
initial population inversion prepared. Besides the production of ultra-short
pulse this frequency comb may have applications towards making short-wavelength
or Tera-hertz lasers.

Optics;Quantum Physics