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Laser Physics

Direct observation of the shift of the 4P(1/2) electronic level in atomic potassium vapor upon the saturation (redistribution of the population of levels) of the 4S(1/2)-4P(3/2) transition under the conditions for nearly resonant laser pumping

V. E. Ogluzdin

Published Aug 1, 2006• 2 citations
Publisher

Abstract

The saturation of the population of transitions can cause the shift of electronic levels of an atomic shell in addition to the Stark effect. Experimental results obtained for atomic potassium vapor and demonstrating a shift of the 4 P (1/2) electronic level upon the saturation of the 4 S (1/2)-4 P (3/2) transition in the presence of the field of a nearly resonant laser pumping are discussed. The processes under study are clearly interpreted based on the classical model of the Lorentz harmonic oscillator, supplemented with data regarding the multiphoton bleaching of the medium in the spectral range under study.

DOI
10.1134/s1054660x06080044

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Journal of Physics B Atomic Molecular and Optical Physics•Nov 27, 2002•23 citations
The saturation of the population of transitions can cause the shift of electronic levels of an atomic shell in addition to the Stark effect. Experimental results obtained for atomic potassium vapor and demonstrating a shift of the 4 P (1/2) electronic level upon the saturation of the 4 S (1/2)-4 P (3/2) transition in the presence of the field of a nearly resonant laser pumping are discussed. The processes under study are clearly interpreted based on the classical model of the Lorentz harmonic oscillator, supplemented with data regarding the multiphoton bleaching of the medium in the spectral range under study.
A theoretical study of the nonlinearity reduction in a four-level system of a potassium atom in the presence of a strong nanosecond laser field, which excites the transition |4S 1/2 ⟩↔|6S 1/2 ⟩ 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 (|4S 1/2 ⟩↔|6S 1/2 ⟩↔|5P 3/2 ⟩↔|4S 1/2 ⟩) emitted parametric fields. For sufficiently high laser intensities and/or atomic densities, the path-1 emitted fields are driven into saturation, a regime accompanied by a substantial population redistribution among the states. Reasonable agreement between earlier experimental results and the theoretical ones is obtained. It is also shown that upon saturation of path-1, for low atomic density, the path-2 (|4S 1/2 ⟩↔|6S 1/2 ⟩↔|4P 3/2 ⟩↔|4S 1/2 ⟩) is activated. A subtle interplay between laser intensity and atomic density may determine the activation of path-2. Also, it is shown that the path-2 emission |6S 1/2 ⟩↔|4P 3/2 ⟩ is an amplified spontaneous emission process which induces a |4P 3/2 ⟩↔|4S 1/2 ⟩ emission, without population inversion, in a cascade scheme.
When an atomic vapor interacts with an intense nearly resonant laser field, the ac Stark effect causes a profound modification of the weak-field absorption spectrum. Two of the induced spectral features can lead to amplification of a weak probe wave. We have previously measured in atomic sodium vapor high probe-wave gain (G = 38) due to the three-photon effect and a somewhat lower gain (G = 4) when the probe wave is detuned from the pump laser frequency by the inverse of the atomic response time.1 We present the results of an experimental and theoretical study of the energy coupling between two intense laser fields of comparable intensity through their interaction with an atomic vapor. In our experiments, a tunable alexandrite laser provides microsecond laser pulses of the required intensity that are nearly resonant with the 4s → 4p transition in potassium. We observed large energy transfer (50%) between the two waves at the nearly degenerate resonance and measured the intensity dependence of the coupling efficiency. Theoretical modeling of the interaction is based on a continued-fraction solution of the density-matrix equations of motion.
The Faraday effect in potassium vapor pumped by nanosecond pulses of near resonant laser radiation is studied experimentally. The input radiation with linewidth 3 cm-1 had a central frequency vp equals 13055 cm-1 which was 12 cm-1 higher than 4S1/2 - 4P3/2 atomic transition frequency v0 equals 13043 cm-1. The strong spectral broadening of pump radiation allowed to observe the Faraday rotation at frequencies v+/- 1 equals v0 +/- 2.5 cm-1 located closer to the atomic resonance where the rotation was high. The decrease of Faraday rotation from 150 degree(s) to 20 degree(s) with the increase of the intensity of pump radiation from 2 (DOT) 105 to 107 W/cm2 has been measured. The saturation of 4S1/2 - 4P3/2 transition is considered as a cause of suppression of Faraday rotation. The contributions of one photon resonance absorption, as well as of multiphoton processes, caused by more intense off resonant part of the broadened pump radiation (having frequency detuning 12 cm-1), to saturation of resonant transition is discussed. The experimental results are compared with theoretical calculations performed.
We report observations of 4‐wave and 6‐wave mixing processes based upon two‐photon pumping of the potassium 4S→6S and 4S→4D transitions in a sodium‐potassium mixture. Additionally we observe coherent emissions at the potassium 3D→4P transition frequencies for pump wavelengths between 725 and 760 nm. The excitation spectra for these emissions show several broad peaks, each of roughly 10 nm width. A series of sharp dips is superimposed on the most intense peak due to depletion of the 3D population by laser‐induced absorption to Rydberg F levels. Although the 3D→4P emissions can be observed in both the forward and backward directions, they are ∼50 times more intense in the forward direction. We believe the forward emission is primarily due to 6‐wave mixing while the backward emission can most likely be attributed to amplified spontaneous emission following two‐photon molecular photodissociation. However, at present, the exact mechanisms responsible for these 3D→4P emissions are not fully understood.
We study the generation of radiation at the 5P3/2‐4S1/2 transition of potassium vapor under excitation of the 4S1/2‐6S1/2 two‐photon resonance. The model consists of the coupled Maxwell‐Bloch equations for a four‐level configuration of Potassium atom including states 4S, 4P, 5P and 6S, which is numerically solved. Previous experimental studies have shown the emission of Parametric Four‐Wave Mixing (PFWM) radiation near the 5P3/2‐4S1/2 transition at low vapor pressures (P<1014 atoms/cm3) which is also shown in the case of the model studied.