We present a theoretical study on the nonlinear behaviors of the electromagnetically induced transparency
resonance subject to two microwave driving fields in a four-level atom system. The probe absorption spectrum is
obtained by solving numerically the relevant equations of density matrix. It is shown that there are two pairs of the EIT
windows in the probe absorption spectrum. The two pairs of EIT windows have symmetry with respect to the resonance
frequency of the probe field, and the separation is equal to the Rabi frequency of the resonant microwave driving field.
But in each pair, the splitting of two EIT windows is dominated to the strength of detuning microwave driving field.
The effect of the relative phase on the spectral linewidth of electromagnetically induced transparency is studied in a
Λ-type three-level configuration coupled by double coupling fields and the result is presented in this paper. We show that
the relative phase between the double coupling fields has a great degree of influence on the spectral width of
electromagnetically induced transparency window. The linewidth can be controlled by changing the relative phase.
Particularly, as the double coupling fields have opposite phases, the linewidth of EIT window can be extremely narrow
In this paper we study the coherent transient property of a Λ-three-level system (Ωd = 0) and a quasi- Λ -four-level
system (Ωd>0). Optical switching of the probe field can be achieved by applying a pulsed coupling field or rf field. In
Λ -shaped three-level system, when the coupling field was switched on, there is a almost total transparency of the probe
field and the time required for the absorption changing from 90% to 10% of the maximum absorption is 2.9Γ0 (Γ0 is
spontaneous emission lifetime). When the coupling field was switched off, there is an initial increase of the probe field
absorption and then gradually evolves to the maximum of absorption of the two-level absorption, the time required for the
absorption of the system changing from 10% to 90% is 4.2Γ0. In four-level system, where rf driving field is used as
switching field, to achieve the same depth of the optical switching, the time of the optical switching is 2.5Γ0 and 6.1Γ0,
respectively. The results show that with the same depth of the optical switching, the switch-on time of the four-level system
is shorter than that of the three-level system, while the switch-off time of the four-level system is longer. The depth of the
optical switching of the four-level system was much larger than that of the three-level system, where the depth of the
optical switching of the latter is merely 14.8% of that of the former. The speed of optical switching of the two systems can
be increased by the increase of Rabi frequency of coupling field or rf field.
In a V-shaped three-level double-resonance configuration, there is strong quantum beats superimposed in a nutation
signal in the probe laser response. In this paper, the beats in the dressed state nutation is studied theoretically within
dressed state picture and the result is presented. An important conclusion is that the strong quantum beats in such a
configuration occurred mainly as a result of the intrinsic coherence of the dressed states. Our result extends the coherent
transient study in bared atomic transition to dressed state transitions.
We investigate the quantum interference effects in a cyclic three-level system with a microwave field driving transition between two low levels. By solving the relative density matrix equations of motion, we obtain the absorption profile of the probe field and identify the conditions under which gain may develop. We demonstrate numerically that the absorption line shape depends on the ratio of the intensities of coupling and driving microwave field. When the intensity of coupling field is much weaker than that of driving field, there is a multi-EITs in the probe absorption spectrum. However, if the intensity of both fields is strong, amplification without inversion occurs in different regime of probe frequency. In addition, we predict that larger amplification is obtained when the coupling field is detuned from exact resonance.
In this paper we present a theoretical study of the effect of a microwave field on an EIT feature. The EIT feature is associated with the well-known three-level Λ type configuration where a pump and probe laser field couples two separate optical transitions. In addition to these two laser fields, there is a microwave field which drives one of the two lower levels of the Λ type three-level system to another hyperfine level. The EIT feature is studied as a function of microwave field frequency and intensity. Our results show that the presence of a microwave field can dramatically modify the EIT feature. When microwave is resonant with the hyperfine transition, the EIT feature can be split into two EIT features. When it is off resonant with the hyperfine transition, it causes a frequency shift of the EIT feature, reminiscent of the well-known light shift effect.
The width of an electromagnetically induced transparency (EIT) resonance is studied theoretically for an ideal three-level system in a L-type configuration. The optical Bloch equations are solved and the power broadening behavior of the EIT resonance is studied as a function of both couple and probe laser intensities over a broad range. It is shown that at relative low couple laser intensity there is a quadratic dependence of the EIT width on the couple laser Rabi frequency and at large couple laser intensity the EIT resonance evolve into the well known dynamic Stark splitting and its width has a linear dependence on the couple Rabi frequency. The dependence of the EIT width on the probe laser intensity shows different characteristics with the dependence on the couple laser intensity. Furthermore, the probe laser causes saturation and this is also discussed in this paper.