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IEEE Journal of Quantum Electronics

Enhanced and stimulated multiphoton processes in free atoms

Shaul Yatsiv, Mehran Naghizadeh rokni, S. Barak

Published Nov 1, 1968• 29 citations
Publisher

Abstract

An enhanced two-photon emission has been observed between the 6S and the 4S levels of potassium. The priming field is the stimulated electronic Raman emission at 2720 cm-1due to scattering of ruby laser radiation from the4P_{3/2}state in potassium. The intense emission at the complementary frequency ω2is close to the 5P → 4S resonance lines. As a result, the coupling coefficient has a resonance character that is favorable for the enhancement. The observed results are compared with a simple analysis. The relation of the enhanced emission with two-quantum absorption, stimulated Raman effect, and parametric four-photon processes is discussed.

DOI
10.1109/jqe.1968.1074980

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Two-photon resonant optical processes in atomic potassium

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Two-photon resonant optical processes, using potassium ns2S1/2 states (7 ≤ n ≤ 20), are investigated in detail by a pulsed dye laser. About 100 coherent lines between 288–422 nm are generated through the processes ωUV ± ωIR = 2ωL and [Formula: see text]. The strongest lines (near mP–4S transitions) are formed by parametric oscillation and are generally split into components that are frequency shifted relative to atomic transitions. About 70 lines are generated by six-wave mixing processes and 15 other lines by four-wave mixing processes. The wavelengths, relative intensities of the lines, and the components of the strongest lines are explained with a theoretical analysis based on the wave equation, atomic polarization, and phase-match condition for both wave-mixing processes and parametric oscillations.

Canadian Journal of Physics•Dec 1, 1984•10 citations
An enhanced two-photon emission has been observed between the 6S and the 4S levels of potassium. The priming field is the stimulated electronic Raman emission at 2720 cm-1due to scattering of ruby laser radiation from the4P_{3/2}state in potassium. The intense emission at the complementary frequency ω2is close to the 5P → 4S resonance lines. As a result, the coupling coefficient has a resonance character that is favorable for the enhancement. The observed results are compared with a simple analysis. The relation of the enhanced emission with two-quantum absorption, stimulated Raman effect, and parametric four-photon processes is discussed.
Stimulated and enhanced two-photon emissions from excited states in potassium have been observed. This emission is primed by stimulated electronic Raman radiation generated by scattering of a giant pulse ruby radiation. Four-photon parametric processes also take place. The two processes can be distinguished by tuning the laser frequency. Most of the emitted radiations are plane-polarized. A pumping model is proposed explaining the required population inversions and the polarization properties of the radiations.
The interaction of a laser with potassium atoms is investigated by monitoring the radiation of the 5P-4S transition under the two-photon 4S(1/2)-6S(1/2) excitation. For low number density and laser intensity the observed radiation is parametric axial or conical, depending on the laser detuning from the two-photon resonance, the number density and the laser intensity. With increasing laser intensities and number densities, an additional delayed component is observed corresponding to a two-step four-wave mixing with the participation of internally generated photons. A two-photon quantum interference effect is observed for the total (axial and conical) parametric four-wave mixing emission. A deviation from the proposed model under certain experimental parameters is attributed to a two-step four-wave mixing and the phase mismatch of the parametric processes.
The competition of stimulated Raman scattering (SRS) between 4S-(5P)-5S and 4S-(3D)-5S channels has been observed as a laser is tuned near the 4S-5P resonance in potassium vapour. The experimental results show that SRS only occurs in the 4S-(5P)-5S channel. In this Raman scattering, suppression of the amplified spontaneous emission (ASE) (5S-4P) has been observed. The influence of the four-wave mixing (FWM) processes on the SRS is discussed. In the 4S-(5P)-3D channel, in the backward direction no detectable emission corresponding to SRS (4S-(5P)-3D) has been observed, so the forward (5P)-3D emission should be FWM, not SRS. The ASE (3D-4P) arises from the ASE (5P-3D), which can be observed in the backward direction.
The authors have studied extensively the stimulated emission at 691.1 nm and 693.9 nm identified as 6S-4P 1/2 , 3/2 transitions in potassium. The origin of the emission is thought to be four-wave parametric emission induced by hybrid transitions. The stimulated emission is enhanced by cascading transitions, the presence of nearby atomic states, stimulated electronic Raman scattering and molecular background signal. Excitation, absorption and emission measurements indicate that bound-bound NaK(X-B) transitions play a dominant role. The rate of energy transfer NaK to K is evaluated as k ET approximately=2.3*10 -9 cm 3 s -1 .
Two-photon resonant optical processes, using potassium ns2S1/2 states (7 ≤ n ≤ 20), are investigated in detail by a pulsed dye laser. About 100 coherent lines between 288–422 nm are generated through the processes ωUV ± ωIR = 2ωL and [Formula: see text]. The strongest lines (near mP–4S transitions) are formed by parametric oscillation and are generally split into components that are frequency shifted relative to atomic transitions. About 70 lines are generated by six-wave mixing processes and 15 other lines by four-wave mixing processes. The wavelengths, relative intensities of the lines, and the components of the strongest lines are explained with a theoretical analysis based on the wave equation, atomic polarization, and phase-match condition for both wave-mixing processes and parametric oscillations.