Optical free induction memory in potassium vapor under a partially-truncated two-photon excitation

Abstract

We numerically study the conditions under which a memory is induced in a sample of potassium vapor by a two-photon partially-truncated excitation field detuned from resonance. We assume a four-level atom and solve numerically the appropriate equations observing the time dependence of the coherence 12 in order to determine the region of the proper parameters: two-photon detuning, the external field intensity, and the atomic density. Subsequently we investigate the stability and the 'read-out' process of the optical free induction memory.

Emissions from high-density potassium atoms excited by either nanosecond or femtosecond laser pulses

“…The internally generated fields have frequencies ω 24 , ω 41 , ω 23 and ω 31 , respectively. These frequencies are related to the corresponding transitions |6S 1/2 ↔ |5P 3/2 , |5P 3/2 ↔ |4S 1/2 , |6S 1/2 ↔ |4P 3/2 and |4P 3/2 ↔ |4S 1/2 [9][10][11][12]. The atomic system Hamiltonian H (I) I in the interaction picture has the following form:…”

“…In the slowly varying envelope approximation (SVEA) for the axially forward propagating waves the Maxwell equations, in terms of the Rabi frequency, can be written as: ∂/∂ζ(Ω mn (ζ, τ )) = i(k mn /4ε 0 )μ nm p mn (ζ, τ ), where p mn (ζ, τ ) = N Tr(μρ) is the quantum mechanical polarization, k mn is the wave number of each transition, N is the atomic density and μ nm is the matrix element of the electric dipole operator for the single-photon transitions [9][10][11][12]. The propagation equations for the internally generated Rabi frequencies can be obtained in the following general form: ∂/∂ζ(Ω mn (ζ, τ )) = iN(k mn /2ε 0 )μ 2 nm σ mn (ζ, τ ), with {m, n} = {2, 4}, and the propagation length was ζ L = 17 cm.…”

“…In the theoretical approach we have used the appropriate approximations presented in [9][10][11][12]. The potassium atom is modelled by a four-level configuration, as shown in Fig.…”

“…In addition, Δ ij = v ij − ω ij describes the detuning from the transition |i ↔ |j , where v ij is the frequency of the electric field related to the transition |i ↔ |j (with {i, j } = {1, 4} and i = j ). From the von Neumann equationρ = −i/ [H (I) I , ρ] in the rotating wave approximation (RWA), a system of 16 density matrix equations was formed [9][10][11][12], where the coherence decay rates were added phenomenologically, taking into account the contribution of elastic collision dephasing rates γ col [4,11,12].…”

“…Thus, the nonlinear wave mixing in gaseous media [1][2][3] has been widely used for a variety of applications, such as the frequency conversion of laser radiation, the optical quantum memory induction and the internal emission of strong coherent fields [4][5][6][7][8][9][10][11][12]. Parametric light generation [1,13], stimulated hyper Raman scattering (SHRS), amplified spontaneous emission (ASE) [1,3], six-and four-wave mixing (FWM) [2,8,14,15] and third-harmonic generation [16] are the most widely studied nonlinear processes that take place in these atomic systems.…”