Axial and conical parametric emissions from potassium atoms under two-photon fs excitation

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

“…As was stated in [6,9,11,12,15], the two-photon excitation of the transition |4S 1/2 ↔ |6S 1/2 of potassium atoms can lead to the emission of coherent (or partially coherent) radiation involving the intermediate states |5P 3/2,1/2 and |4P 3/2,1/2 (i.e. the dominant relaxation paths are connected with the states |4 and |3 ), respectively.…”

“…In [15] we had presented a collection of results concerning the spectra, the excitation spectra (peak intensity at |5P 3/2,1/2 ↔ |4S 1/2 as a function of two-photon detuning) and the far-field pattern of the emitted radiation near the potassium transition |5P 3/2,1/2 ↔ |4S 1/2 for fs excitation of the potassium twophoton transition. We verified the parametric nature of the radiation of interest, because no backward component was detected.…”

“…The experimental set-up used for the fs excitation of atomic potassium was similar to that presented in [15]. The atomic potassium was confined inside a heated cylindrical stainlesssteel cell.…”

“…In addition, the laser-atom interaction, with co-propagating beams, may result in destructive quantum interference (QI) between the pump and emitted radiation, in the ns (nanosecond) or fs (femtosecond) excitation case [1-9, 11, 12, 15]. It was observed, both experimentally and theoretically, that internally generated fields are also connected with various resonant and near-resonant nonlinear processes in atomic gases, such as sodium and potassium [1,3,6,7,15]. Therefore, to treat properly the resonant nonlinear processes in metal vapours, it is often necessary to include in the analysis not only the externally injected photon field, but also the generation and interaction with fields that evolve internally from the nonlinear polarizations, induced by the external laser field.…”

“…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. In addition, the laser-atom interaction, with co-propagating beams, may result in destructive quantum interference (QI) between the pump and emitted radiation, in the ns (nanosecond) or fs (femtosecond) excitation case [1-9, 11, 12, 15].…”