A Comparative Study of Coherent and Incoherent Drives in Four-Level Quantum Dot-Based Spaser

TL;DR

This study compares the effects of coherent and incoherent pumping on a four-level quantum dot-based spaser, revealing that incoherent pumping better sustains continuous operation and affects the resonance characteristics.

Contribution

It provides a detailed analytical comparison of coherent versus incoherent pumping in a quantum dot spaser, highlighting the advantages of incoherent excitation for continuous mode operation.

Findings

Incoherent pump leads to earlier LSP oscillation and higher steady-state N_n.

Resonance peak position is unaffected by pump type.

Peak amplitude depends on pump rate.

Abstract

In this article, we theoretically investigate a spaser (surface plasmon amplification by stimulated emission of radiation), which consists of a spherical silver nanoparticle surrounded by four-level gain medium of quantum dots (QDs). The spaser system is pumped coherently and incoherently with the same excitation rate, and the characteristics of coherent localized surface plasmon (LSP) mode, thus produced, are compared for the two pumping scenarios. We provide a detailed analytical expression for the steady state and show that the incoherent pump is more suitable for the continuous spaser mode. The reason is better understood by studying the temporal evolution of number of LSP (N_n ), where the oscillation of LSP starts early for incoherent drive and relaxes to steady state with a large value of N_n. At a large pump rate, spaser curve shows saturation. In addition, we have found that the resonance peak of spaser field is independent of coherent as well as incoherent pumping, while the peak amplitude of field depends on the pump rate.