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AIP conference proceedings

Emissions in potassium vapour under 4S[sub 1∕2]–7S[sub 1∕2] two-photon nsec excitation

Dionysios Pentaris, George Chatzikyriakos, A. Armyras, Thomas Efthimiopoulos, Nikolaos A. Vainos, Stelios Couris, Emmanuel Paspalakis, Ioannis B. Koutselas, Stavros Pissadakis

Published Jan 1, 2010• 2 citations
Publisher

Abstract

The two‐photon excitation of 4S1/2–7S1/2 transition of potassium atoms is studied. Several coherent emissions and processes are possible, such as parametric four‐wave (PFWM), parametric six‐wave (PSWM) mixing and competition with the stimulated hyper Raman (SHRS) and the amplified spontaneous emission (ASE). The radiations at the transitions 6P3/2,1/2−4S1/2, 6S1/2−4P3/2,1/2 and 5P3/2,1/2−4S1/2 are emitted only in the forward direction (indicating a parametric process), while the radiation at the transition 4P3/2,1/2−4S1/2 is emitted in the forward and in the backward direction, indicating an ASE process.

DOI
10.1063/1.3521352

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AIP conference proceedings•Jan 1, 1988•1 citation
The two‐photon excitation of 4S1/2–7S1/2 transition of potassium atoms is studied. Several coherent emissions and processes are possible, such as parametric four‐wave (PFWM), parametric six‐wave (PSWM) mixing and competition with the stimulated hyper Raman (SHRS) and the amplified spontaneous emission (ASE). The radiations at the transitions 6P3/2,1/2−4S1/2, 6S1/2−4P3/2,1/2 and 5P3/2,1/2−4S1/2 are emitted only in the forward direction (indicating a parametric process), while the radiation at the transition 4P3/2,1/2−4S1/2 is emitted in the forward and in the backward direction, indicating an ASE process.
Abstract\nWe investigate the emissions of atomic potassium excited by two photons near the 4S1/2-6S1/2 transition. Radiation near the 6S1/2-4P3/2, 1/2 and 4P3/2, 1/2-4S1/2 transitions are studied for the unidirectional and the bidirectional cases respectively. It is shown that the total output intensity increases considerably for the bidirectional propagation. This is attributed to the effective increase of the Doppler free excitation and the cancellation of the quantum interference effect that is associated with the multiple paths of excitation of certain states. Keywords. Counter-propagating beams, amplified spontaneous emission (ASE), stimulated hyper Raman scattering (SHRS), parametric four-wave mixing (PFWM).
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 and one below the potassium 4P3/2 level are reported. Radiation emitted below the 4P3/2 - 4S1/2 level is due to a Parametric Four Wave Mixing (PFWM) process initiated by the internally generated radiation from 5P3/2 - 4S1/2 level. The line emitted close to the 4P3/2 level is produced by a two-step Four Wave Mixing (FWM) process. Direct one photon driving of 4S3/2 - 4P3/2 transition produces similar to HEP radiation.
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.
It is shown that by proper use of the excitation spectra, the emission spectra of the transition and the far-field patterns it is possible to distinguish between competing processes involved in the two-photon excitation to the 6S state of potassium, namely: (a) resonant fluorescence emission associated with the cascading spontaneous emission (ASE) and (b) the four-wave mixing parametric process. The effect of the buffer gas on the intensities of the spectra of the radiations emitted is discussed. Conical emission and spatial instabilities of the excitation radiation and the emission were also observed for high excitation and high vapour pressure of potassium.
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.