Dynamics of Plasmonic Stopped-Light Nanolasing and Condensation
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Dynamics of Plasmonic Stopped-Light Nanolasing and Condensation 1
A. Freddie Page , Tim W. Pickering1, Joachim M. Hamm1, Sebastian M. Wuestner1 and Ortwin Hess1 Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom 1
ABSTRACT By reducing the number of dimensions that light can propagate in from three down to two, one may gain control over the characteristics of propagation. This control can allow for “Stopped Light” (SL), where wavepackets of light are slowed down to a zero group velocity. This is achieved by designing planar metal-dielectric structures that are stacked in one dimension allowing for waveguide modes in the other two, and engineering the dispersion relation of these structures. Stopped light structures can be further optimized to reduce their dispersion and increase the number of spatial frequencies supported, which allows for confinement of electromagnetic energy over volumes smaller than the diffraction limit over fixed regions in space. If this electromagnetic energy is confined over a region that provides gain, the question arises, can amplification of this light energy occur? and indeed can a regime of lasing be entered into? We show that stopped light lasing is indeed possible, despite there being no resonant cavity in 2d to confine the light, and explore the properties of this new type of laser.
INTRODUCTION Lasers are made possible by the interaction of two fundamental processes - gain and feedback. Gain is the provision of stimulated emission of photons (or indeed plasmons) which will allow for the coherent amplification of electromagnetic energy. Gain media that are available includes semiconductors in bulk [1], quantum wells [2], as well as organic laser dye molecules [3]. The other component is feedback, i.e. the mechanism by which emitted light repeatedly interacts with the the gain medium in order to stimulate further emission. Usually feedback is provided by a resonant cavity, the modes of which have a strong overlap with the gain profile. A number of cavity designs have been constructed in nano-optics including crystal defect modes [4], microcavity resonators [5] and even the highly asymmetric, multiple scattering cavity of a “random laser” [6]. An alternative scheme of providing feedback is in stopped-light lasing (SLL) [7] which does not rely on a cavity to confine light, but rather forms wavepackets, with zero group velocity, over the gain medium. Stopped light can be achieved in nano-plasmonic structures where light is confined in a waveguide mode in one dimension and free to propagate in the other two. The waveguide dispersion can be engineered such that the power flow in metal and dielectric layers becomes equal and opposite forcing the light to stop.
THEORY Planar-layered plasmonic heterostructures support a variety of waveguide modes, hosting surface plasmon polaritons at each metallic interface. The dispersion relation, Ȧ(q), of the modes of the structure is controlled by the particular configuration of the layers. In such stru
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