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Journal of the Physical Society of Japan

Up-Converted Luminescence of a Two-Level Molecule with Population Inversion

Ryosuke Hata, Nobuhiko Yokoshi, Hiroshi Ajiki, Hajime Ishihara

Published Aug 25, 2014• 2 citations
Publisher

Abstract

We theoretically study a novel up-converted luminescence from a two-level molecule coupled with an auxiliary system such as an anharmonic LC resonator and a metallic nano-antenna. The auxiliary system is assumed to be strongly driven by a continuous wave laser so that a Mollow triplet appears in the luminescent spectrum. When the peak energy of the upper Mollow triplet sideband is tuned to the molecular excited level, the intensity of the up-converted luminescence is considerably enhanced. At the same time, the population of the two-level molecule is inverted. We also discuss the conditions for high photoemission efficiency in the up-converted luminescence under a highly inverted population. This result indicates the potential applications in future single-molecule lasers.

DOI
10.7566/jpsj.83.093401

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Abstract A novel technique for up‐converted luminescence generation from a two‐level molecule via population inversion is studied using the quantum toy model; this model is used to represent a coupled‐molecule and metallic nano‐antenna system sustaining a localized surface plasmon polariton (LSPP). The metallic nano‐antenna is assumed to have anharmonicity, reflecting experimentally observed results. The system is driven by a strong, offresonant, and Gaussian pulse laser so that the LSPP exhibits a Mollow triplet spectrum. When the two‐level molecular resonance is tuned to the upper Mollow triplet sideband, the molecular‐level population is inverted. We discuss the population dynamics, the Purcell effect, and the up‐converted luminescence activity of the two‐level molecule. These results indicate the potential applications of the present system in novel coherent light sources. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
We theoretically propose a new method for generating up-converted coherent light from two-level systems (TLSs) coupled with a plasmonic nanocavity. The emission spectrum of a TLS excited by a strong laser exhibits a triplet structure called the Mollow triplet. If the lower Mollow sideband is tuned to the cavity mode energy, population inversion of a TLS occurs. When the driving laser is abruptly truncated under this condition, an up-converted photon is emitted from the TLSs. We also predict the up-converted superfluorescence from an ensemble of TLSs as a correlation effect among the excited states of the TLSs.
Coherent light sources pumped by external fields require multi-level systems to achieve a population inversion and they always convert an input frequency into lower one. In their paper on pp. 105–108, Hata and coworkers, however, theoretically proposed a frequency up-conversion luminescence from a two-level system with inverted population. The two-level system interacts with a metallic nano-antenna sustaining a localized surface plasmon-polariton. The obtained result shows that a strong and off-resonant Gaussian pulse laser with optimum peak intensity realizes the population inversion of the two-level system, which generates the up-converted luminescence. This demonstration indicates the potential applications of the present system in novel coherent light sources.
We theoretically investigate photoexcitation processes of a two-level molecular system coherently coupled with an antenna system having a significant dissipation. The auxiliary antenna enables the whole system to exhibit anomalous optical effects by controlling the coupling with the molecule. For example, in the weak excitation regime, the quantum interference yields a distinctive energy transparency through the antenna, which drastically reduces the energy dissipation. On the other hand, in the strong excitation regime, a population inversion of the two-level molecule appears due to the nonlinear effect. Both phenomena can be explained by regarding the antenna and molecule as one quantum-mechanically coupled system. Such an approach drives further research to exploit the full potential of the coupled systems.
We investigate properties of a two-level atom coupled to a single cavity mode, and driven by a strong, in general off-resonance, external field. The cavity field is tuned to resonance with a Mollow sideband. We show that the steady-state atomic population may be highly (nearly totally) inverted, a phenomenon forbidden in semiclassical theory, and that a strong enhancement of the resonance fluorescence results. This system is suggested as an alternative approach to create the atomic inversion necessary for laser or maser generation without using additional atomic levels. We also investigate properties of the cavity field, derive an analytical expression for the photon number distribution in the good cavity or strong-coupling limit, and discuss the conditions under which this system acts as a single-atom dressed-state laser.
Abstract The population transfer dynamics in a strongly driven two-level system is studied. It is shown that population inversion can be efficiently achieved when a laser pulse whose photon energy is about half of the energy separation of the two levels is turned on suddenly. This situation is realized when a neutral atom or molecule is ionized at the peak of the laser field, followed by the laser-driven population transfer among two states of an atomic or molecular ion. The mechanism of the efficient population transfer for an ion effectively exposed to a laser field with a sudden turn-on is examined by numerical calculations based on the quasi-stationary Floquet theory.