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

Abstract

Dependence of amplification without inversion (AWI) on the relative strength of probe and coherent field Rabi frequencies has been studied in H 2 and LiH molecules for three-level Λ configuration. We have derived exact analytical expressions for coherences and populations keeping all the orders of probe field Rabi frequency (G) and coherent field Rabi frequency (Ω) in the steady state limit. Previously, first-order approximation (i.e. keeping only the first-order term in G) was used and hence AWI was studied for the condition Ω G. Here, by using the exact analytical expressions of coherences and populations, we have shown that AWI is maximum when Ω is within the same order of probe field Rabi frequency G irrespective of the choice of different ro-vibrational transitions in both the molecules. However, the shape of the gain profile and the maximum value of gain on the probe field and the absorption on coherent field depend on the choice of different ro-vibrational levels as the upper lasing levels. Effect of bidirectional pumping, homogeneous and inhomogeneous broadening on AWI process has been studied. By solving the density matrix equations numerically it has been shown that both the transient and the steady state AWI can be obtained and the numerical values of coherences and populations at large time are in very good agreement with exact analytical values in the steady state limit. It has been shown that in molecules AWI can be obtained on probe field of smaller wavelength than that of the coherent field which has not been observed in atoms so far.

Control over group velocity in a three-level closed Λ system via spontaneously generated coherence and dynamically induced coherence

“…Thus, the system with upper state A 1 + (v = 0, j = 2) and the lower dressed states |+ , |− behaves as a system with antiparallel dipole moments. The spontaneous decay widths (γ + and γ − ) can be calculated from dipole transition moments (d 2+ and d 2− ) and frequencies of transition [49][50][51]. This system has the advantage that the magnitudes of the dipole transition moments (d 2+ and d 2− ) and the energy separation between dressed states (S ) can be controlled by the Rabi frequency (S) and detuning of the driving laser field ( L ).…”

“…In this paper, we show theoretically the effect of both SGC [19,20,46,47] and DIC [48][49][50][51] on the susceptibility and the group index of a closed three-level system in the presence of incoherent pumping. In a three-level system two of the levels are coupled by a coherent field and the probe field is applied between one of these two levels and a third level (i.e., ground state or a lower level).…”

Broadening of EIT window by incoherent pumping in a three-level Λ system: Effect of homogeneous and inhomogeneous broadening

“…As mentioned before the spacing between two dressed levels (|+ and |− ) can be adjusted to be greater than the homogeneous/inhomogeneous width (by controlling S and ∆ L ). Usually in small molecules the homogeneous width becomes three orders of magnitude greater than the individual spontaneous decay width [23,34]. Here the individual spontaneous decay widths are on the order of ≈ 10 −13 a.u.…”

“…It is well known that the dephasing due to the decay to other vibrational levels can be reduced by properly choosing a repumping scheme [37]. Previously we have shown that to obtain amplification without population inversion with homogeneous broadening one will have to increase the Rabi frequencies by three orders of magnitude [23,34,38]. Let us now examine how the EIT can be achieved in the presence of homogeneous and inhomogeneous broadening.…”

“…In this case EIT occurs due to the cancellation of absorption (from one coherence) by emission (from other) when the contributions to the probe response from two coherences, i.e. the spontaneously generated coherence [20,21] and the dynamically induced coherence [20][21][22][23], are equal and opposite at resonance. For transmission of the probe light with large spectral width different schemes have been proposed and experimentally investigated [24][25][26].…”