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

Abstract

A study of the emissions, for high atomic density potassium, under nanosecond (ns) or femtosecond (fs) twophoton excitation is presented. It is shown that the parametric emissions (connected to the |6S 1/2 ↔ |5P 3/2 ↔ |4S 1/2 transitions) strongly depend on the excitation intensity and they have a nonlinear and a linear response region, in both kinds of excitation. In the ns excitation, the calculated results of a four-level atomic configuration agree well with the experimental ones, in the case of the path-1 parametric emissions (|6S 1/2 ↔ |5P 3/2 ↔ |4S 1/2 ) for certain excitation and atomic density parameters. Also, the fields of the atomic path-2 (|6S 1/2 ↔ |4P 3/2 ↔ |4S 1/2 ) are numerically shown to be amplified spontaneous emission (ASE) or cascade ASE without population inversion, due to the population transfer to the |6S 1/2 level initially and its subsequent collapse to the lower levels. In the fs excitation, only parametric emissions are observed from both atomic paths and there are not yet numerical calculations available to compare D. Pentaris ( ) · T. Efthimiopoulos Laser,

Control of the emission channels energy flow in a nonlinear laser–potassium atom interaction

“…In some cases the flow of the excitation energy, through the available atomic channels, can be adjusted giving rise to interesting phenomena. Phenomena such as population trapping [2,5,[7][8][9][10], coherently controlled atomic transitions [3,4,11,12] and quantum interference (QI) between available excitation channels and channels of emission [13,[18][19][20][22][23][24][25] have been extensively studied in the past.…”

“…In recent studies [18][19][20][21][22][23][24][25], the nonlinear interaction of a laser pulse with an alkali atom (potassium) was analysed, focusing on the generation of new coherent or partially coherent fields, by wave mixing processes. Coherent parametric four-wave mixing (PFWM), partially coherent stimulated hyper Raman scattering (SHRS) and amplified spontaneous emission (ASE) result from such nonlinear interactions.…”

“…Coherent parametric four-wave mixing (PFWM), partially coherent stimulated hyper Raman scattering (SHRS) and amplified spontaneous emission (ASE) result from such nonlinear interactions. In addition, a destructive QI takes place on the state |6S 1/2 between the resonant two-photon laser excitation and the internally emitted fields [19,[22][23][24][25]. As a result, the emission response on both transitions of path-1 in potassium, |6S 1/2 ↔ |5P 3/2 ↔ |4S 1/2 exhibits a linear dependence on the excitation laser intensity [19].…”