The focus of the present thesis is on two topics: the first is the interaction of surface plasmons and active media, and the second is acoustic metamaterials. These two seemingly different topics are connected by the notion that the negative material responses can lead to surface states. Surface plasmons are surface electromagnetic waves on metal surfaces, a consequence of negative permittivity. The study of active plasmonics is two fold: firstly, we study the surface plasmon amplification to compensate the intrinsic metal losses; secondly we study the enhanced spontaneous emission of emitters in excited state close to the metal surfaces. The concept of metamaterials—periodic composite structures with resonating element as a unit cell—is extended to acoustics. These acoustic metamaterials provide effective negative material responses and therefore the new surface states.

We first propose a simple analytical method to obtain explicit expressions for surface plasmon polariton (SPP) dispersion, propagation length and critical gain required to overcome losses. A multiple quantum well structure is proposed to study SPP amplification accounting for SPP polarization, refractive index and temperature effects. In addition, we show that the emission of an optical emitter into various channels—surface plasmons, lossy surface waves and free radiation—can be precisely controlled by strategically positioning the emitters close to the metal surfaces. Next, we report a direct experimental evidence of stimulated emission of SPP at telecom wavelengths (1532 nm) in a SPP waveguide geometry using erbium doped phosphate glass. Together—the theoretical and experimental studies—these could provide a range of photonic devices; for example, nanolasers, surface plasmon amplifiers and efficient emitters.

We investigate the acoustic analogue of electromagnetic metamaterials, and we report an ultrasonic metamaterial consisting of an array of subwavelength Helmholtz resonators that exhibits negative modulus. With the freedom of design that these acoustic metamaterials provide, we propose a new surface wave on an acoustic metamaterial with effective negative mass density. We further extend the concept of metamaterials to shear horizontal transverse waves. We provide a design of elastic metamaterial that exhibits effective negative mass density, and we finally show that pure shear surface elastic wave is possible with elastic metamaterials of negative shear modulus. We believe that this new class of acoustic and elastic metamaterials offers interesting applications like materials with dispersive properties, negative index and sub-diffraction limited imaging.