Four-wave mixing and parametric four-wave mixing near the 4P 4S transition of the potassium atom

Abstract

Potassium 4S1/2–6S1/2 two-photon excitation initiates the emission of several internally generated photons. For the first time two emission lines, one close to and one below the potassium 4P3/2 level, are reported for low pumping intensity. Radiation emitted below the 4P3/2 level is due to a parametric four-wave mixing process that uses the photons emitted at the 5P3/2–4S1/2 transition and a two-step four-wave mixing process generates the line emitted close to the 4P3/2 level.

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

“…We notice that both path-2 fields are generated 13 ns after the laser pulse maximum ( figure 9(b, c)), a characteristic which is quite different compared to the temporal profiles of the emissions from path-1. As we see in figure 10 the commencement of the path-2 emissions corresponds to the minimum population of the ground state 1 , which also coincides with the maximum population transfer to states 2 [17].…”

Action of counter-propagating laser beams on two-photon excitation of potassium vapour

“…and a low excitation intensity. As it was shown [12] there is some differentiation in the relative intensities of the I HEP and I LEP components with the twophoton detuning indicating the different generation processes involved (one-step and two-step processes correspondingly).…”

“…The spectrum of the radiation has two main peaks: a high energy peak (I HEP ) near 766.5 nm and a low energy peak (I LEP ) near 766.6 nm respectively. According to a proposed model [12] the two peaks of the radiation near the 4P 3/2 -4S 1/2 transition have a different origin. In particular the I HEP is a product of a parametric process along with the 693.9 nm emission.…”

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

“…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]. 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.…”