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 the lL;g symmetry of the H 2 molecules can be obtained when the lowest AI state of the lL;g symmetry is pumped incoherently. We have considered a resonant two-photon transition scheme from the ground X1L;g(v O,j 1) state to the ionization continuum embracing the two AI states (the lowest and the first excited autoionizing states) of the 1 L;g symmetry via the resonant intermediate B 1 L;u (v 4, j 2) level. The effect of two-photon nearresonant autoionizing channels via the near-resonant rovibrationallevels of the B 1 L;u 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 the B 1 L;u 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 rovibrationallevels leads to the increase in gain around the resonances with two AI states from the B1L;u (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.PACS 42.55.Ah -General laser theory. PACS 42.50.Hz -Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift.

Control of amplification without inversion in H2 and LiH molecules: Dependence on relative magnitude of probe and coherent field Rabi frequencies in three-level Λ system

“…We found that the values of populations and coherences obtained by solving the density matrix equations numerically at large time are in good agreement with the values obtained from the exact expressions in the steady state limit. However, results obtained with first-order approximation agree with the numerical results only when Ω G. AWI were studied theoretically either by choosing different parameters for the process [12,13] or in real systems like atoms [14,15] and molecules [3][4][5][16][17][18]. The presence of rotational and vibrational states makes the study of LWI/AWI fascinating in molecules as these states influence the process of inversionless lasing.…”

“…However, the lasers used should have bandwidth short enough to avoid resonant excitation from other vibrational levels. Earlier, our group has studied AWI in H 2 molecule using resolvent operator technique [3][4][5], in which the dependence of gain on the choice of different vibrational levels was also shown considering the effect of two-photon near-resonant transitions to autoionizing states (the upper lasing level). In a recent calculation [20] on three-level ladder, V and Λ system in H 2 and Li 2 molecules we have shown that AWI can be obtained in VUV, and in violet region respectively from the first excited Rydberg state when two of the levels are coupled by a strong coherent field.…”

“…Amplification without inversion (AWI) and lasing without inversion (LWI) have been studied both theoretically [1][2][3][4][5] and experimentally [6,7] in three, four and multilevel systems by choosing different configurations, e.g. ladder, V , Λ etc.…”