12 results found
Page AF, Hamm J, Hess O, 2018, Polarization and plasmons in hot photoexcited graphene, Physical review B: Condensed matter and materials physics, Vol: 97, ISSN: 1098-0121
We present a robust and exact method for calculating the polarization function and plasmon dispersion of graphene, for an arbitrary (isotropic) non-equilibrium carrier distribution, within random phase approximation (RPA). This is demonstrated for a range of carrier distributions, includinghot carrier distributions which occur within the femtoseconds following photoexcitation. We show that qualitatively different behaviour from the equilibrium case can occur. As the polarization function determines dynamic screening, its calculation shall be essential to quantifying carrier-carrier scattering channels for graphene far from equilibrium.
Bello F, Page AF, Pusch A, et al., 2017, Combining ε-Near-Zero Behavior and Stopped Light Energy Bands for Ultra-Low Reflection and Reduced Dispersion of Slow Light., Scientific Reports, Vol: 7, ISSN: 2045-2322
We investigate media which exhibits epsilon-near-zero (ENZ) behavior while simultaneously sustaining stopped light energy bands which contain multiple points of zero group velocity (ZGV). This allows the merging of state-of-the-art phenomena that was hitherto attainable in media that demonstrated these traits separately. Specifically, we demonstrate the existence of Ferrell-Berreman (FB) modes within frequency bands bounded by points of ZGV with the goal to improve the coupling efficiency and localization of light in the media. The FB mode is formed within a double layer, thin-film stack where at subwavelength thicknesses the structure exhibits a very low reflection due to ENZ behavior. In addition, the structure is engineered to promote a flattened frequency dispersion with a negative permittivity able to induce multiple points of ZGV. For proof-of-concept, we propose an oxide-semiconductor-oxide-insulator stack and discuss the useful optical properties that arise from combining both phenomena. A transfer matrix (TM) treatment is used to derive the reflectivity profile and dispersion curves. Results show the ability to reduce reflection below 0.05% in accordance with recent experimental data while simultaneously exciting a polariton mode exhibiting both reduced group velocity and group velocity dispersion (GVD).
Page AF, 2016, Surface Plasmon Emission and Dynamics in Active Planar Media
By reducing the number of dimensions that light can propagate in from three to two, control over the properties of propagation can be achieved. The plasmonic modes of planar metal-dielectric heterostructures will confine light in one dimension, enhancing the electromagnetic fields within the structure. This thesis focuses on two particular aspects of active nanoplasmonics in planar systems, stopped light lasing and plasmons with gain in nonequilibrium graphene.For stopped-light lasing, a plasmonic waveguide mode is designed to have two points of zero group velocity in a narrow frequency range, in order to increase the local density of optical states that a gain medium can emit into. The two stopped light points form a band of slow light that supports a wide range of wavevectors, allowing localisation over a sub-wavelength gain medium and providing the feedback required for lasing. This results in a new type of laser that does not rely on predefined cavity modes, in fact is cavity-free in 2d, dynamically forming its lasing mode about a locally pumped region of carrier inversion.Graphene, a single-atom thick semimetal, provides the ultimate miniaturisation as a truly 2d material. It is shown that graphene can support plasmons with gain, under realistic conditions of collision loss, temperature, doping, and carrier relaxation via amplified spontaneous emission. This is made possible by developing a scheme to evaluate polarisabilities for nonequilibrium carrier distributions, allowing the calculation of the exact rpa complex-frequency plasmon dispersion solutions. The rates of spontaneous emission are calculated and are critically dependant on the exact dispersion relation. The instantaneous rates are found to be 5 times faster than previously reported and, when coupled with phonons, lead to carrier relaxations on 100 fs timescales. The polarisability and relaxation rates must form the basis of any active graphene device, where electromagnetic energy is coupled to an ev
Hamm JM, Page AF, Bravo-Abad J, et al., 2016, Nonequilibrium plasmon emission drives ultrafast carrier relaxation dynamics in photoexcited graphene, Physical Review B, Vol: 93, ISSN: 1550-235X
The fast decay of carrier inversion in photoexcited graphene has been attributed to optical phonon emission and Auger recombination. Plasmon emission provides another pathway that, as we show here, drives the carrier relaxation dynamics on ultrafast timescales. In studying the nonequilibrium relaxation dynamics we find that plasmon emission effectively converts inversion into hot carriers, whose energy is then extracted by optical phonon emission. This mechanism not only explains the observed fs-lifetime of inversion but also offers the prospect for atomically thin ultrafast plasmon emitters.
Page AF, Ballout F, Hess O, et al., 2016, Plasmons of Hot-Carrier Graphene, 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 268-270
Page AF, Guazotti S, Hamm JM, et al., 2015, Plasmonic Stopped-Light Lasing: From Cavity-Free Nanolasing to Nonlinear-Self-Structuring in Surface-Plasmon Polariton Condensation
Designed stopped-light singularities in the density of optical states of a planar gain-enhanced nanoplasmonic waveguide structure provide a new stopped-light feedback mechanism that allows for cavity-free nanolasing and nonlinear self-structuring in surface-plasmon polariton condensation.
Page AF, Ballout F, Hess O, et al., 2015, Amplification and Spontaneous Emission of Plasmons in Photo-Inverted Graphene -METAMATERIALS 2015, 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 244-246
Wuestner S, Pickering TW, Hamm JM, et al., 2015, Ultrafast dynamics of nanoplasmonic stopped-light lasing, Faraday Discussions, Vol: 178, Pages: 307-324, ISSN: 1359-6640
We study the spatio-temporal dynamics of coherent amplification and lasing in planar gain-enhanced nanoplasmonic structures and show that a singularity in the density of optical states leads to a stopped-light feedback mechanism that allows for cavity-free photonic and surface-plasmon polariton nanolasing. We reveal that in the absence of cavity-induced feedback a phase-locked superposition of a quasi dispersion-free waveguide mode promotes the dynamic formation of a subwavelength lasing mode. Simulations on the basis of a full-time domain Maxwell-Bloch Langevin approach uncover a high spontaneous emission factor [small beta] [approximate] 0.9 and demonstrate that the stopped-light lasing/spasing mechanism is remarkably robust against interface roughness. Stopped-light surface-plasmon polariton lasing is shown to be stable for gain sections of a width of down to 200 nm but in wider gain structures of the order of 1 [small mu ]m the dynamics is characterised by spatio-temporally oscillating lasing surface-plasmon polaritons with typical temporal and spatial periods of smaller than 5 fs and smaller than 100 nm. Stopped-light lasing thus provides opportunities for ultrafast nanolasing and the realization of ultra-thin lasing surfaces and offers a new route to ultrafast spasing and cavity-free active quantum plasmonics.
Pickering TW, Hamm JM, Page AF, et al., 2014, Cavity-free plasmonic nanolasing enabled by dispersionless stopped light, Nature Communications, Vol: 5, Pages: 4972-4972, ISSN: 2041-1723
Tsakmakidis KL, Pickering TW, Hamm JM, et al., 2014, Completely Stopped and Dispersionless Light in Plasmonic Waveguides, Physical Review Letters, Vol: 112, Pages: 167401-167401, ISSN: 0031-9007
Pickering T, Hamm JM, Page AF, et al., 2014, Stopped-Light Nanolasing in Hybrid Plasmonic Waveguides, 16th International Conference on Transparent Optical Networks (ICTON), Publisher: IEEE, ISSN: 2162-7339
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