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Physical Review A

Enhancement and control of a coherent localized surface plasmon through pump-pulse engineering

Ankit Purohit, Akhilesh Kumar Mishra

Published Jun 4, 2024• 1 citation
Publisher

Abstract

This article investigates a spaser geometry in which a silver nanoparticle is enclosed by \ensuremath{\Lambda}-type three-level gain media in the form of quantum dots. An intense Gaussian pump pulse induces population transfer in this \ensuremath{\Lambda}-type quantum dot gain medium. The transition energy from the gain medium is transferred to the nearby localized surface-plasmon (LSP) mode of the silver nanoparticle, resulting in a highly intense and coherent generation of LSPs. We demonstrate that an optimum value of pump-pulse width and pulse amplitude is required for an intense and coherent LSP generation. A Gaussian pump pulse can lead to Gaussian-shape temporal and spectral LSP profiles. However, as the pump pulse broadens, the Gaussian-shape LSP profile gets distorted, resulting in less intense and asymmetric temporal as well as spectral profiles. In practice, detuning typically exists between the pump frequency and the transition frequency of the quantum dot energy levels. Consequently, employing adiabatic rapid passage phenomena through a linearly chirped Gaussian pulse emerges as an effective technique for ensuring robust population transfer within the energy levels of the quantum dots. This further enhances the number of LSPs. Furthermore, the study addresses the effect of detuning noise in the output of the spaser system. Thus, a shaped pump pulse also enables manipulation of the temporal and spectral profiles of LSPs.

DOI
10.1103/physreva.109.063505

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This article investigates a spaser geometry in which a silver nanoparticle is enclosed by \ensuremath{\Lambda}-type three-level gain media in the form of quantum dots. An intense Gaussian pump pulse induces population transfer in this \ensuremath{\Lambda}-type quantum dot gain medium. The transition energy from the gain medium is transferred to the nearby localized surface-plasmon (LSP) mode of the silver nanoparticle, resulting in a highly intense and coherent generation of LSPs. We demonstrate that an optimum value of pump-pulse width and pulse amplitude is required for an intense and coherent LSP generation. A Gaussian pump pulse can lead to Gaussian-shape temporal and spectral LSP profiles. However, as the pump pulse broadens, the Gaussian-shape LSP profile gets distorted, resulting in less intense and asymmetric temporal as well as spectral profiles. In practice, detuning typically exists between the pump frequency and the transition frequency of the quantum dot energy levels. Consequently, employing adiabatic rapid passage phenomena through a linearly chirped Gaussian pulse emerges as an effective technique for ensuring robust population transfer within the energy levels of the quantum dots. This further enhances the number of LSPs. Furthermore, the study addresses the effect of detuning noise in the output of the spaser system. Thus, a shaped pump pulse also enables manipulation of the temporal and spectral profiles of LSPs.
In this paper, we investigate the interaction between the three-level Λ-type quantum dot (QD)-based gain medium and the dipolar localized surface plasmon (LSP) mode of a silver nanoparticle. Previously, we demonstrated that a linearly chirped Gaussian pump pulse can enhance the peak value of the number of LSPs, provided there exists a detuning between the Gaussian pulse central frequency and the energy levels of QDs [ Phys. Rev. A 109 , 063505 ( 2024 ) PLRAAN 1050-2947 10.1103/PhysRevA.109.063505 ]. We explored both time-independent and time-harmonic detuning scenarios, elucidating their effects on the spaser emission. Expanding upon this work, here we present a study showcasing the impact of specially designed V- and Λ-shape chirped Gaussian pump pulses on stimulating the intense LSP. We conduct a comparative analysis of the spaser dynamics with differently shaped pump pulses: unchirped, linear chirped (both positive and negative), and specially designed Λ- and V-shape chirps. The study reveals that with time-independent detuning, a Gaussian pulse with a V-shape chirp performs better. Conversely, with harmonic time-dependent detuning, Λ-shape chirp is more effective for a certain noise frequency range.
Abstract In this article, we theoretically investigate a spaser (surface plasmon amplification by stimulated emission of radiation) comprising a spherical silver nanoparticle surrounded by a four-level gain medium of quantum dots. The spaser system is pumped coherently and incoherently with the same excitation rate, and the characteristics of the resultant coherent localized surface plasmon (LSP) mode are compared for the two pumping scenarios. We provide a detailed analytical expression for the steady state and demonstrate that the incoherent pump is more suitable for the continuous spaser mode. The reason is better understood by studying the temporal evolution of the number of LSPs N n , where the LSP oscillation starts earlier for an incoherent drive and relaxes to a steady state with a large value of N n . At a large pump rate, the spaser curve shows saturation. In addition, we have found that the resonance peak of the spaser field is independent of coherent and incoherent pumping, whereas the peak amplitude of the field depends on the pump rate.
We investigate surface plasmon amplification in a silver nanoparticle coupled to an externally driven three-level gain medium and show that quantum coherence significantly enhances the generation of surface plasmons. Surface plasmon amplification by stimulated emission of radiation is achieved in the absence of population inversion on the spasing transition, which reduces the pump requirements. The coherent drive allows us to control the dynamics and holds promise for quantum control of nanoplasmonic devices.
Abstract Quantum coherence and interference offer novel pathways to control light–matter interaction at the atomic scale, with enticing prospects in both fundamental and applied science. Here, we demonstrate coherent control over transient excitation of localized surface plasmon modes of a silver nanosphere adjacent to a quantum coherence medium composed of three-level quantum emitters, using a theoretical approach. We show that quantum interference enables more than two orders of magnitude enhancement in the surface plasmon field generated when the quantum emitters are driven coherently, in comparison to incoherent pumping. Furthermore, under optimal conditions, intense surface plasmon lasing can be induced without population inversion on the spasing transition. Our results open up the possibility of overcoming dissipative losses in plasmonic modes in the transient regime when steady-state population inversion is difficult to achieve due to fast relaxation rates and impractical pumping requirements.
We investigate the relaxation dynamics of a quantum dipole emitter (QDE), e.g., a molecule or quantum dot, located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. A generic three-level QDE, which is pumped with an external laser pulse and thereby brought into an optically active excited state, is considered to be weakly coupled to the resonant LSP described by a coherent state. It is shown that, under the condition of the QDE-MNP characteristic relaxation time being much shorter than that of the QDE in free space but much longer than the LSP lifetime, the QDE relaxation dynamics can be described analytically and feature, in general, non-exponential decay with complicated transient behaviour. The main physical consequence of this relaxation process is that the emission, being largely determined by the MNP, comes out with a substantial delay. It is also shown that energy dissipation in the QDE-MNP system is relatively weak with the probability of the photon emission being ∼0.75, a number which, rather surprisingly, does not explicitly depend on the metal absorption characteristics. A large number of QDE-MNP system parameters in our analytical description open new possibilities for controlling quantum emitter dynamics.