  We discuss the propagation of laser radiation through a medium of quantum
prepared {\Lambda}-type atoms in order to enhance the insight into the physics
of QS-PT generator suggested in Phys. Rev. A 80, 035801 (2009). We obtain
analytical results which give a qualitatively corerct description of the
outcoming series of ultrashort optical pulses and show that for the case of
alkali vapor medium QS-PT generation may be implemented under ordinary
experimental conditions.
