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The Journal of Chemical Physics

Up-conversion superfluorescence induced by abrupt truncation of coherent field and plasmonic nanocavity

Ryosuke Hata, Nobuhiko Yokoshi, Hiroshi Ajiki, Hajime Ishihara

Published Dec 11, 2019• 3 citations
Publisher

Abstract

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.

DOI
10.1063/1.5128020

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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.
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 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.
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 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.
We present a quantum theory of a coherently pumped two-level atom in a photonic crystal, coupled to both a multi-mode wave-guide channel and a high quality micro-cavity embedded within the photonic crystal. The cavity field characteristics are highly distinct from that of a corresponding high Q cavity in ordinary vacuum. If the cavity field mode is resonant with the central component of the Mollow spectrum of atomic resonance fluorescence, enhanced, inversionless, nearly coherent light generation occurs when the photon density of states jump between the Mollow spectral components is large. The spectrum of the cavity field is also investigated and showed to be narrower than in the case of a conventional cavity. Moreover, enhanced, non-classical light generation is possible, if the cavity field is tuned on resonance with a Mollow sideband.
A superfluorescence effect in a V-type medium with initial Raman inversion, driven by a strong coherent field on one of the transitions, is studied analytically and numerically. It is shown that the collective spontaneous emission evolves in the presence of a minor population of an upper state of a superfluorescent transition. In the limit of the Rabi frequency of a driving field large compared to that of a superfluorescent pulse, the system of two equations for the fields and density-matrix equations for three states of the medium is reduced to Maxwell-Bloch equations for an effective two-level system. The shape of a superfluorescent pulse is perfectly described in terms of a slowly varying envelope function (which is a solution of the Maxwell-Bloch equations), filled with fast oscillations associated with Rabi floppings on the driving transition. In the average, i.e., after integrating over a period of Rabi oscillations, the upper superfluorescent state is populated less than other states, such that the phenomenon may be called ``superfluorescence without inversion'' by analogy with lasing without inversion.