Nonlinear susceptibilities of two-level systems in intense double-frequency fields (A)

A. Rahelia, M. Sahraib, A. Namdarc +1 more

A theoretical scheme for enhanced Kerr nonlinearity is proposed in a four-level ladder-type atomic system based on double dark resonances (DDRs). We solve the relevant density matrix equations in steady state and utilize the perturbation theory to obtain the analytical expressions for the third order susceptibility of the atomic system. The influence of system parameters on behavior of the first and third order susceptibilities is then discussed. In particular, it is found that an enhanced Kerr nonlinearity with reduced linear and nonlinear absorption is obtained around zero probe detuning under the slow light condition through proper adjusting the laser field intensity and frequency detuning of driving fields. The dressed state analysis is employed to explain the physical origin of the obtained result. The obtained results may be important for all-optical signal processing and quantum information technology.

Nikolai L. Manakov, S. I. Marmo, A. G. Faǐnshteǐn

P N Butcher, David Cotter

In earlier chapters we have considered in detail the susceptibility formalism of nonlinear optics, which is perhaps the most familiar approach and has a wide range of application. Starting from the constitutive relations of Chapter 2, the susceptibility formalism is quite general. In many practical applications, a particular phenomenon can be described accurately by a single order of nonlinearity, and the susceptibility then provides a useful and convenient description. However, this is not always the case. Some of the most interesting phenomena in nonlinear optics involve close resonance with the transition frequencies of the medium, and perhaps also the use of very intense optical fields. As remarked in §4.5, in these circumstances the resonant susceptibilities display mathematical divergences which are clearly unphysical. Strictly, these divergences occur only because higher-order nonlinearities have been neglected. Successive orders of nonlinearity take into account such effects as saturation, power broadening and level shifts (optical Stark effect). For intense fields or very close resonance, the contributions from several orders of nonlinearity may be comparable in magnitude. Therefore, despite its generality, the susceptibility formalism does not necessarily provide the most practical approach for the description of resonant processes. This chapter is concerned with the problem of deriving alternative and more manageable descriptions of resonant nonlinear processes, illustrated by examples. For much of the chapter, the nonlinear medium is treated as a two-level system (described in §6.2).

A. E. Kaplan

N. F. Perel'Man

José Luis Paz, M. Gorayeb, A. J. Hernández

It was studied the solvent influence over a two level system in the four wave mixing spectroscopy. the solvente effect was incorporated to the model in a stochastic form, through the broadening of the upper molecular level. Two intense waves of the same frequency, ω1, and another wave with minor intensity and ω2 frequency, were considered coupled to the nonlinear system, generating a new signal whose frequency is ω3, and where the wave-vectors follow the relation vector k1 + vector k1 = vector k2 + vector k3. Using the dipolar-electric and the rotating wave approximations, it was calculated the average of the coherence at the ω1, ω2 and ω3 frequencies. From that results, analytical expressions to the susceptibilities at the studied frequencies were obtained. Linear, coherent and coupled processes were identified.