Electromagnetically induced transparency by internally generated fields under two-photon excitation

This work investigates the generation of amplified spontaneous emission (ASE) without population inversion in the 4P₃2/-4S₁2/ transition of the potassium atom under two-photon excitation of the atom from the 4S₁2/ to the 6S₁2/ state. The calculations show that the radiation observed in the 4P₃2/-4S₁2/ transition is generated without population inversion for a broad range of the parameters used. It seems that a V-type scheme due to the 5P₃2/-4S₁2/ emission and a cascade scheme due to the 6S₁2/-4P₃2/ emission are both important in the generation of the radiation in the 4P₃2/-4S₁2/ transition. Both schemes are examined and compared with the experimental results in order to assess their impact in the generation of ASE without population inversion.