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European Quantum Electronics Conference (EQEC)

Electromagnetically induced transparency by internally generated fields under two-photon excitation

Nikolaos Merlemis, Thomas Efthimiopoulos, M. Katharakis, A. Lyras

Published Jan 18, 2006• 0 citations
Publisher

Abstract

This work investigates the generation of amplified spontaneous emission (ASE) without population inversion in the 4P/sub 3/2/-4S/sub 1/2/ transition of the potassium atom under two-photon excitation of the atom from the 4S/sub 1/2/ to the 6S/sub 1/2/ state. The calculations show that the radiation observed in the 4P/sub 3/2/-4S/sub 1/2/ transition is generated without population inversion for a broad range of the parameters used. It seems that a V-type scheme due to the 5P/sub 3/2/-4S/sub 1/2/ emission and a cascade scheme due to the 6S/sub 1/2/-4P/sub 3/2/ emission are both important in the generation of the radiation in the 4P/sub 3/2/-4S/sub 1/2/ transition. Both schemes are examined and compared with the experimental results in order to assess their impact in the generation of ASE without population inversion.

DOI
10.1109/eqec.2005.1567255

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arXiv:1701.00232•Journal of the Optical Society of America B•Nov 7, 2017•22 citations
This work investigates the generation of amplified spontaneous emission (ASE) without population inversion in the 4P/sub 3/2/-4S/sub 1/2/ transition of the potassium atom under two-photon excitation of the atom from the 4S/sub 1/2/ to the 6S/sub 1/2/ state. The calculations show that the radiation observed in the 4P/sub 3/2/-4S/sub 1/2/ transition is generated without population inversion for a broad range of the parameters used. It seems that a V-type scheme due to the 5P/sub 3/2/-4S/sub 1/2/ emission and a cascade scheme due to the 6S/sub 1/2/-4P/sub 3/2/ emission are both important in the generation of the radiation in the 4P/sub 3/2/-4S/sub 1/2/ transition. Both schemes are examined and compared with the experimental results in order to assess their impact in the generation of ASE without population inversion.
We report the experimental observation of the amplified spontaneous emission (ASE) generated at the 4P 3/2 –4S 1/2 transition of potassium atoms following the excitation of the 4S 1/2 –6S 1/2 two-photon transition. We propose that the amplification of the observed radiation is inversionless, due to driving fields on neighbouring transitions that are not imposed externally, but are internally generated in the medium. A theoretical model based on the density operator formalism is presented, which confirms that the radiation observed in the 4P 3/2 –4S 1/2 transition is generated without population inversion for a broad range of the parameters used. It seems that a self-generated ladder scheme is the dominant mechanism, but other schemes are also examined and compared with the experimental results in order to assess their impact on the generation of the inversionless 4P 3/2 –4S 1/2 emission.
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.
A numerical study, stimulated by existing experimental results concerning the temporal dynamics of internally generated radiations, is presented for a four-level system of the potassium atom. An intense nanosecond duration laser pulse excites the two-photon transition and initiates the generation of internal radiations from quantum noise. It is shown that the temporal profiles of the generated radiations along the atomic path-1, ( ) and path-2, ( ), evolve differently as a function of certain system parameters. It is also shown that the excitation laser intensity affects the parametric emissions along path-1 and the population of the states. The path-2 emissions, which also depend on the excitation laser intensity, are most probably due to amplified spontaneous emission (ASE), without population inversion, in the case of strong excitation. We finally examine the radiation dynamics under the effect of the elastic dephasing collisions between the potassium atoms with the buffer gas atoms.
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.
Population inversion on the 5D5/2−6P3/2 transition in rubidium atoms produced by cw laser excitation at different wavelengths has been analyzed by comparing the generated mid-infrared radiation at 5.23 μm originating from amplified spontaneous emission (ASE) and isotropic blue fluorescence at 420 nm. Using a novel method for detection of two-photon excitation via ASE, we have observed directional co- and counter-propagating emission at 5.23 μm. Evidence of a threshold-like characteristic is found in the ASE dependences on laser detuning and Rb number density. The power dependences of the backward- and forward-directed emission can be very similar; however, their spectral dependences are not identical. A new type of temporally and spatially coherent radiation is suggested.