Laser Driven Two-Level System

In this section, we consider a laser driven two-level system described by the Hamiltonian operator of Eq. (6.3), in the basis 1 , 2) of eigenstates of Hq 

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Laser Driven Two-Level System Transforming Eq.(6.16) yields... 

Transitions with parallel or antiparallel dipole moments can be created not only in multilevel systems but also in a two-level system driven by a polychromatic field [63]. In order to show this, we consider a two-level atom driven by a bichromatic field composed of a strong resonant laser field and a weaker laser field detuned from the atomic resonance by the Rabi frequency of the strong field. The effect of the strong field alone is to produce dressed states [35]... 

If the laser pulse applied to the sample molecules is sufficiently long and intense, a molecule (represented by a two-level system) will be driven back and forth between the two levels at the Rabi flopping frequency (Vol. 1, (2.96)). The time-dependent probability amplitudes ai (t) and 02 (0 are now periodic functions of time and we have the situation depicted in Vol. 1, Fig. 2.23. Since the laser beam is alternately absorbed (induced absorption E E2) and amplified (induced emission 2 i). the intensity of the transmitted beam displays an oscillation. Because... 

Paspalakis and Knight [28] have considered a V-type three-level system driven from an auxiliary level by two laser fields of the same frequencies. They have predicted linewidth narrowing and cancellation of the fluorescenc, which can be controlled via the phase difference between the two laser fields used for the excitation. Ghafoor et al. [29] have considered a four-level system in which quantum interference can be generated by three driving fields and have shown that the linewidths and intensities of the spectral lines can be controlled by the phases and amplitudes of the driving fields. 

B. Glushko, B. Kryzhanovsky Radiative and collisional damping effects on efficient population transfer in a three-level system driven by two delayed laser pulses, Phys. Rev. A 46 (1992) 2823. 

Consider the Menon-Agarwal approach to the Autler-Townes spectrum of a V-type three-level atom. The atom is composed of two excited states, 1) and 3), and the ground state 2) coupled by transition dipole moments with matrix elements p12 and p32, but with no dipole coupling between the excited states. The excited states are separated in frequency by A. The spontaneous emission rates from 1) and 3) to the ground state 2) are Tj and T2, respectively. The atom is driven by a strong laser field of the Rabi frequency il, coupled solely to the 1) —> 2) transition. This is a crucial assumption, which would be difficult to realize in practice since quantum interference requires almost parallel dipole moments. However, the difficulty can be overcome in atomic systems with specific selection rules for the transition dipole moments, or by applying fields with specific polarization properties [26]. 

The phase independent quantum interference through the multiple Raman transitions in the three-level A-type system can also be realized in a four-level double A-type system with a similar laser coupling scheme depicted in Fig. 6. The four-level double-A-type system is driven by two... 

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