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Applied Physics Letters

Complete characterization of the spasing (L-L) curve of a three-level quantum coherence enhanced spaser for design optimization

Lakshitha Kumarapperuma, Malin Premaratne, Pankaj Kumar Jha, Mark I. Stockman, Govind Prasad Agrawal

Published May 14, 2018• 25 citations
Publisher

Abstract

We demonstrate that it is possible to derive an approximate analytical expression to characterize the spasing (L-L) curve of a coherently enhanced spaser with 3-level gain-medium chromophores. The utility of this solution stems from the fact that it enables optimization of the large parameter space associated with spaser designing, a functionality not offered by the methods currently available in the literature. This is vital for the advancement of spaser technology towards the level of device realization. Owing to the compact nature of the analytical expressions, our solution also facilitates the grouping and identification of key processes responsible for the spasing action, whilst providing significant physical insights. Furthermore, we show that our expression generates results within 0.1% error compared to numerically obtained results for pumping rates higher than the spasing threshold, thereby drastically reducing the computational cost associated with spaser designing.

DOI
10.1063/1.5025354

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We demonstrate that it is possible to derive an approximate analytical expression to characterize the spasing (L-L) curve of a coherently enhanced spaser with 3-level gain-medium chromophores. The utility of this solution stems from the fact that it enables optimization of the large parameter space associated with spaser designing, a functionality not offered by the methods currently available in the literature. This is vital for the advancement of spaser technology towards the level of device realization. Owing to the compact nature of the analytical expressions, our solution also facilitates the grouping and identification of key processes responsible for the spasing action, whilst providing significant physical insights. Furthermore, we show that our expression generates results within 0.1% error compared to numerically obtained results for pumping rates higher than the spasing threshold, thereby drastically reducing the computational cost associated with spaser designing.
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 present a theoretical discussion on the feasibility of spasing for a specific spaser setup. For this purpose we develop a numerically exact and feasible solution to the open system Tavis-Cummings model in the Born- Markov Lindblad formalism. The complexity of the solution scales with the third power in the number of two level systems- a considerable advance compared to the exponential scaling of the brute force solution. The question of spasing is answered negatively in agreement with the literature.
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.
We present an analytical description of ultrashort femtosecond pump–probe experiments and investigate the gain response of quantum dot (QD) semiconductor optical amplifiers. The calculation provides a full analytical solution of numerical studies to recent experiments in such structures (Gomis-Bresco et al 2008 Phys. Rev. Lett. 101 256803). Our approach is based on QD Bloch equations, which are analytically evaluated within the third-order temporal perturbation theory (χ (3) level). In particular, we study the influence of the coherence and the population dynamics of two confined QD levels on the gain as a function of the delay time between the pump and the probe pulse. We discuss how to engineer optimal conditions for high-performance QD amplifiers, which are characterized by an ultrafast gain recovery and a pronounced gain depletion.
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.