On amplification of radiation emitted from the excited autoionizing state of the H2 molecule in the presence of incoherent pumping to the lowest autoionizing state

Abstract

We have shown that the amplification without population inversion (AWOPI) from the first excited autoionizing (AI) state of the1Σg symmetry of the H2 molecules can be obtained when the lowest AI state of the1Σg symmetry is pumped incoherently. We have considered a resonant two-photon transition scheme from the groundX1Σg(v = 0;j = 1) state to the ionization continuum embracing the two AI states (the lowest and the first excited autoionizing states) of the1Σg symmetry via the resonant intermediateB1Σu(v = 4;j = 2) level. The effect of two-photon near-resonant autoionizing channels via the near-resonant rovibrational levels of theB1Σu state has also been considered. We have found that the gain can be obtained in different spectral regions corresponding to the resonances with the lowest and first excited AI states from the intermediate levels of theB1Σu state. The inherent coherence between two AI states due to the configuration interaction coupling via the common continuum has been found to have a significant effect on the amplification process, which occurs around all the resonance frequencies connecting this AI state with the intermediate levels. This gain can be significantly modified by increasing the coupling strength of this excited AI state with the continuum. Moreover, the gain from the excited AI state remains unaffected by the damping caused by incoherent pumping to the lowest AI state. It has also been shown that the persistence of inversionless gain from the excited AI state is shorter than that from the lowest AI state. The presence of close-lying near-resonant rovibrational levels leads to the increase in gain around the resonances with two AI states from theB1Σu (v = 4;j = 2) level. The advantages of this type of scheme are: i) AWOPI can be obtained from an excited AI state although it has not been pumped and ii) the amplification obtained from the excited AI state is almost unaffected by the distortion caused by incoherent pumping to the lower AI state.