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Register a new userResolving closely spaced levels for Doppler mismatched double resonance
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Added by
Elijah Ogaro Nyakang'o
Publication date
2021
fields
Physics
and research's language is
English
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In this paper, we present experimental techniques to resolve the closely spaced hyperfine levels of a weak transition by eliminating the residual/partial two-photon Doppler broadening and cross-over resonances in a wavelength mismatched double resonance spectroscopy. The elimination of the partial Doppler broadening is based on velocity induced population oscillation (VIPO) and velocity selective saturation (VSS) effect followed by the subtraction of the broad background of the two-photon spectrum. Since the VIPO and VSS effect are the phenomena for near zero velocity group atoms, the subtraction gives rise to Doppler-free peaks and the closely spaced hyperfine levels of the $6text{P}_{3/2}$ state in Rb are well resolved. The double resonance experiment is conducted on $5text{S}_{1/2}rightarrow5text{P}_{3/2}$ strong transition (at 780~nm) and $5text{S}_{1/2}rightarrow6text{P}_{3/2}$ weak transition (at 420~nm) at room temperature.
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The angular distribution and linear polarization of the fluorescence light following the resonant photoexcitation is investigated within the framework of the density matrix and second-order perturbation theory. Emphasis has been placed on signatures for determining the level sequence and splitting of intermediate (partially) overlapping resonances, if analyzed as a function of the photon energy of the incident light. Detailed computations within the multiconfiguration Dirac-Fock method have been performed especially for the $1s^{2}2s^{2}2p^{6}3s;, J_{i}=1/2 ,+, gamma_{1} :rightarrow: (1s^{2}2s2p^{6}3s)_{1}3p_{3/2};, J=1/2, , 3/2 :rightarrow: 1s^{2}2s^{2}2p^{6}3s;, J_{f}=1/2 ,+, gamma_{2}$ photoexcitation and subsequent fluorescence emission of atomic sodium. A remarkably strong dependence of the angular distribution and linear polarization of the $gamma_{2}$ fluorescence emission is found upon the level sequence and splitting of the intermediate $(1s^{2}2s2p^{6}3s)_{1}3p_{3/2};, J=1/2, , 3/2$ overlapping resonances owing to their finite lifetime (linewidth). We therefore suggest that accurate measurements of the angular distribution and linear polarization might help identify the sequence and small splittings of closely-spaced energy levels, even if they can not be spectroscopically resolved.
A quantum-mechanical formulation of energy transfer between closely-spaced surfaces is given. Coupling between the two surfaces arises from the atomic dipole-dipole interaction involving transverse-photon exchange. The exchange of photons at resonance greatly enhances the radiation transfer. The spacing (distance) dependence is derived for the quantum well - quantum well situation. The interaction between two planar quantum wells, separated by a gap is found to be proportional to the 4th power of the wavelength-to-gapwidth ratio and to the radiation tunneling factor for the evanescent waves. Expressions for the net power transfer, in the near-field regime, from hot to cold surface for this case is given and evaluated for representative materials. Computational modeling of selected, but realizable, emitter and detector structures and materials shows the benefits of both near-field and resonance coupling (e.g., with 0.1 micron gaps).
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A quantum-mechanical formulation of energy transfer between closely spaced surfaces is given. Coupling between the two surfaces arises from the atomic dipole-dipole interaction involving transverse-photon exchange. The exchange of photons at resonance enhances the radiation transfer. The interaction between two surfaces, separated by a gap, is found to be dependent upon geometric, material, frequency, dipole, and temperature factors, along with a radiation-tunneling factor for the evanescent waves. The derived geometric term has a gap-spacing (distance) dependence that varies inversely as the second power for bulk samples to the inverse fourth power for the quantum well - quantum well case. Expressions for the net power transfer, in the near-field regime, from hot to cold surface for this case is given and evaluated for representative materials.
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