A review of nanoplasmonics is given. This includes fundamentals, nanolocalization of optical energy and hot spots, ultrafast nanoplasmonics and control of the spatiotemporal nanolocalization of optical fields, and quantum nanoplasmonics (spaser and gain-assisted plasmonics). This article reviews both fundamental theoretical ideas in nanoplasmonics and selected experimental developments. It is designed both for specialists in the field and general physics readership.

Nanoplasmonics: past, present, and glimpse into future

Nanoplasmonics has recently experienced explosive development with many novel ideas and dramatic achievements in both fundamentals and applications The spaser has been predicted and observed experimentally as an active element—a generator of coherent local fields Even greater progress will be achieved if the spaser can function as an ultrafast nanoamplifier—an optical counterpart of the MOSFET (metal–oxide–semiconductor field effect transistor) A formidable problem with this is that the spaser has inherent feedback, causing quantum generation of nanolocalized surface plasmons and saturation and consequent elimination of the net gain, making it unsuitable for amplification We have overcome this inherent problem and shown that the spaser can perform functions of an ultrafast nanoamplifier in two modes: transient and bistable On the basis of quantum density matrix (optical Bloch) equations we have shown that the spaser amplifies with gain with a switching time  fs (potentially, ~10 fs) This prospective spaser technology will further broaden both fundamental and applied horizons of nanoscience, in particular enabling ultrafast microprocessors working at 10–100 THz clock speed Other prospective applications are in ultrasensing, ultradense and ultrafast information storage, and biomedicine The spasers are based on metals and, in contrast to semiconductors, are highly resistive to ionizing radiation, high temperatures, microwave radiation, and other adverse environments

http://physics.gsu.edu/stockman/data/Stockman_JOPT_2010_Spaser_Nanoamplifier.pdf

The spaser as a nanoscale quantum generator and ultrafast amplifier

We analyze the transmission and reflection data obtained through transfer matrix calculations on metamaterials of finite lengths, to determine their effective permittivity epsilon and permeability micro. Our study concerns metamaterial structures composed of periodic arrangements of wires, cut wires, split ring resonators (SRRs), closed SRRs, and both wires and SRRs. We find that the SRRs have a strong electric response, equivalent to that of cut wires, which dominates the behavior of left-handed materials (LHM). Analytical expressions for the effective parameters of the different structures are given, which can be used to explain the transmission characteristics of LHMs. Of particular relevance is the criterion introduced by our studies to identify if an experimental transmission peak is left or right handed.

Effective medium theory of left-handed materials

On the basis of a full-vectorial three-dimensional Maxwell-Bloch approach we investigate the possibility of using gain to overcome losses in a negative refractive index fishnet metamaterial. We show that appropriate placing of optically pumped laser dyes (gain) into the metamaterial structure results in a frequency band where the nonbianisotropic metamaterial becomes amplifying. In that region both the real and the imaginary part of the effective refractive index become simultaneously negative and the figure of merit diverges at two distinct frequency points.

/pdf/overcoming-losses-with-gain-in-a-negative-refractive-index-hxxbm4gdcj.pdf

Overcoming Losses with Gain in a Negative Refractive Index Metamaterial

We report on near infrared semiconductor nanopatch lasers with subwavelength-scale physical dimensions (0.019 cubic wavelengths) and effective mode volumes (0.0017 cubic wavelengths). We observe lasing in the two most fundamental optical modes which resemble oscillating electrical and magnetic dipoles. The ultra-small laser volume is achieved with the presence of nanoscale metal patches which suppress electromagnetic radiation into free-space and convert a leaky cavity into a highly-confined subwavelength optical resonator. Such ultra-small lasers with metallodielectric cavities will enable broad applications in data storage, biological sensing, and on-chip optical communication.

Subwavelength metal-optic semiconductor nanopatch lasers

A bulk left-handed metamaterial with fishnet structure is investigated to show the optical loss compensation via surface plasmon amplification with the assistance of the gain medium of PbS quantum dots. Simultaneously negative permittivity and permeability are confirmed at the telecommunication wavelength (1.5 μm) by the retrieval of the effective electromagnetic property. The dependence of enhanced transmission on the gain coefficient, as well as on the propagation layers, demonstrates that ultralow loss is feasible in bulk left-handed metamaterials.

/pdf/optical-loss-compensation-in-a-bulk-left-handed-metamaterial-10p76md3ud.pdf

Optical loss compensation in a bulk left-handed metamaterial by the gain in quantum dots

A bulk left-handed metamaterial with fishnet structure is investigated to show the optical loss compensation via surface plasmon amplification, with the assistance of a Gaussian gain in PbS quantum dots. The optical resonance enhancement around 200 THz is confirmed by the retrieval method. By exploring the dependence of propagation loss on the gain coefficient and metamaterial thickness, we verify numerically that the left-handed response can endure a large propagation thickness with ultralow and stable loss under a certain gain coefficient.

We propose and analyze theoretically a double magnetic plasmon resonance nanolaser, in which ytterbium-erbium codoped material is used as the gain medium. Through design of the double magnetic resonance modes, pumping light (980 nm) can be resonantly absorbed and laser light (1550 nm) can be resonantly generated simultaneously. We introduce a set of rate equations combined to describe the operation of the laser and predict the lasing condition. According to our calculations, the disadvantage that pumping light is difficult to be absorbed by a thin slab of gain materials can be overcome.

https://dsl.nju.edu.cn/dslweb/images/research/plasmonics/mpp_publications/Z.H.Zhu-20090311-APL-Optically%20pumped%20nanolaser%20based%20on%20two%20magnetic%20plasmon%20resonance%20modes.pdf

Optically pumped nanolaser based on two magnetic plasmon resonance modes

We demonstrate that left-handed resonance transmission from metallic metamaterial, composed of periodically arranged double rings, can be extended to visible spectrum by introducing an active medium layer as the substrate. The severe ohmic loss inside metals at optical frequencies is compensated by stimulated emission of radiation in this active system. Due to the resonance amplification mechanism of recently proposed lasing spaser, the left-handed transmission band can be restored up to 610 nm wavelength, in dependence on the gain coefficient of the active layer. Additionally, threshold gains for different scaling levels of the double-ring unit are investigated to evaluate the gain requirement of left-handed transmission restoration at different frequency ranges.

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Z. H. Zhu

Papers

Optical loss compensation in a bulk left-handed metamaterial by the gain in quantum dots

Optical loss compensation in a bulk left-handed metamaterial by the gain in quantum dots

Optically pumped nanolaser based on two magnetic plasmon resonance modes

Resonance amplification of left-handed transmission at optical frequencies by stimulated emission of radiation in active metamaterials

Resonance amplification of left-handed transmission at optical frequencies by stimulated emission of radiation in active metamaterials