Abstract
We model spaser as an n-level quantum system and study a spasing geometry comprising of a metal nanosphere resonantly coupled to a semiconductor quantum dot (QD). The localized surface plasmons are assumed to be generated at the nanosphere due to the energy relaxation of the optically excited electron-hole pairs inside the QD. We analyze the total system, which is formed by hybridizing spaser's electronic and plasmonic subsystems, using the density matrix formalism, and then derive an analytic expression for the plasmon excitation rate. Here, the QD with three nondegenerate states interacts with a single plasmon mode of arbitrary degeneracy with respect to angular momentum projection. The derived expression is analyzed, in order to optimize the performance of a spaser operating at the triple-degenerate dipole mode by appropriately choosing the geometric parameters of the spaser. Our method is applicable to different resonator geometries and may prove useful in the design of QD-powered spasers.
Highlights
The emerging era of nanoplasmonics is expected to improve the speed and efficiency of optical devices, by allowing miniaturization beyond the diffraction limit using surface plasmons in circuits [1,2,3]
It can be observed from Eq (17) that the total plasmon excitation rate of the spaser, Rlp mainly depends on the matrix elements for the electron-hole pair-plasmon interaction, Vsl1pe,ms0pe for each degenerate state and the detuning ∆2p because we assume that matrix element for the pump light-quantum dot (QD) interaction Vs2e,s0e is constant under continuous wave (CW) operation
We studied a simple spaser geometry consists of a metal nanosphere resonantly coupled to a QD
Summary
The emerging era of nanoplasmonics is expected to improve the speed and efficiency of optical devices, by allowing miniaturization beyond the diffraction limit using surface plasmons in circuits [1,2,3]. In order to determine spaser characteristics such as threshold spasing condition, spasing frequency and spaser linewidth, Stockman [5, 18, 19] analyzed the interaction between a metal nanoparticle and closely located chromophores which are modeled as two level systems (TLS). Among the quantum mechanical models of the spaser, the work of Stockman [5, 18, 19] and Protsenko et al [20] are noteworthy They only analyze the quantum states of the active medium assuming it as a TLS. We first find the electric field and the eigenfrequencies of the localized surface plasmon modes in the resonator, characteristics of the active medium, followed by the derivation of the spaser Hamiltonian, which is needed to analyze the spaser kinetics using the density matrix theory. We obtain an expression for the plasmon excitation rate of the spaser, and study how the geometric parameters affect the operation of a dipole spaser
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