Saturation and population transfer of a two-photon excited four-level potassium atom

Abstract

Abstract.A theoretical study of the nonlinearity reduction in a four-level system of potassium, atom in the presence of a strong nanosecond laser field, which excites the transition 1/2 1/2 4S 6S ↔ with two photons, is presented. It is shown, that the destructive quantum interference between the laser field and the internally generated radiations results in a linear response of the atomic path-1 ( 1/2

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

“…The calculated results are compared with the experimental ones, in order to investigate the features and the properties of the atomic path-1 and also the conditions which describe the path-2 emissions (|4S 1/2 ↔ |6S 1/2 ↔ |4P 3/2 ↔ |4S 1/2 ). For the ns excitation, we show that QI and the population distribution depend crucially on the atomic density, as we have partially presented in our previous works [11,12]. For the fs excitation, we present only the experimental results demonstrating the influence of the destructive QI on the path-1 at high atomic densities and we compare the obtained results with the ones taken using ns excitation.…”

“…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.…”

“…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:…”

“…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.…”

“…The fields corresponding to the transitions |6S 1/2 ↔ |5P 3/2 (|2 ↔ |4 ), |5P 3/2 ↔ |4S 1/2 (|4 ↔ |1 ), |6S 1/2 ↔ |4P 3/2 (|2 ↔ |3 ) and |4P 3/2 ↔ |4S 1/2 (|3 ↔ |1 ) are internally generated during the atom-laser interaction and population transfer may lead to significant change of the refraction index and thus can limit the conversion efficiency for the wave mixing process. It is interesting to note that destructive QI can cause a linear response of a nonlinear atomic system [6,9,11,12]. It was also shown that, for the ns excitation of sodium [1][2][3][4][5] and potassium [6,9,11,12] atoms, the pump laser intensity and the atomic density were the crucial factors which determined whether the destructive QI effect is insignificant (nonlinear region) or significant (linear region), respectively.…”