arXiv subjects

R. M. Osgood

Publications and source records attributed to R. M. Osgood.

6 recordsLinked to original sources

arXiv2011

Trapping Surface Electrons on Graphene Layers and Islands

We report the use of time- and angle-resolved two-photon photoemission to map the bound, unoccupied electronic structure of the weakly coupled graphene/Ir(111) system. The energy, dispersion, and lifetime of the lowest three image-potential states are measured. In addition, the weak interaction between Ir and graphene permits observation of resonant transitions from an unquenched Shockley-type surface state of the Ir substrate to graphene/Ir image-potential states. The image-potential-state lifetimes are comparable to those of mid-gap clean metal surfaces. Evidence of localization of the excited electrons on single-atom-layer graphene islands is provided by coverage-dependent measurements.

cond-mat.mes-hall↗

arXiv2009

Observations of zero-order bandgaps in negative-index photonic crystal superlattices at the near-infrared

We present the first observations of zero-n bandgaps in photonic crystal superlattices consisting of alternating stacks of negative index photonic crystals and positive index dielectric materials in the near-infrared. Guided by ab initio three-dimensional numerical simulations, the fabricated nanostructured superlattices demonstrate the presence of zero-order gaps in remarkable agreement with theoretical predictions across a range of different superlattice periods and unit cell variations. These volume-averaged zero-index superlattice structures present a new type of photonic band gap, with potential for complete wavefront control for arbitrary phase delay lines and open cavity resonances.

physics.optics↗

arXiv2008

Achieving sub-diffraction imaging through bound surface states in negative-refracting photonic crystals at the near-infrared

We report the observation of imaging beyond the diffraction limit due to bound surface states in negative refraction photonic crystals. We achieve an effective negative index figure-of-merit [-Re(n)/Im(n)] of at least 380, ~125x improvement over recent efforts in the near-infrared, with a 0.4 THz bandwidth. Supported by numerical and theoretical analyses, the observed near-field resolution is 0.47 lambda, clearly smaller than the diffraction limit of 0.61 lambda. Importantly, we show this sub-diffraction imaging is due to the resonant excitation of surface slab modes, allowing refocusing of non-propagating evanescent waves.

physics.optics↗

arXiv2006

Near-infrared negative-index metamaterials consisting of multiple layers of perforated metal-dielectric stacks

In this paper, we numerically demonstrate a near-infrared negative-index metamaterial (NIM) slab consisting of multiple layers of perforated metal-dielectric stacks and exhibiting low imaginary part of index over the wavelength of negative refraction. The effective index is obtained using two different numerical methods and found to be consistent. Backward phase propagation is verified by calculation of fields inside the metamaterial. These results point to a new design of low loss thick metamaterial at optical frequencies.

physics.optics↗

arXiv2005

Enhanced stimulated Raman scattering in slow-light photonic crystal waveguides

We investigate for the first time the enhancement of the stimulated Raman scattering in slow-light Silicon-on-Insulator (SOI) photonic crystal line defect waveguides. By applying the Bloch-Floquet formalism to the guided modes in a planar photonic crystal, we develop a formalism that relates the intensity of the down-shifted Stokes signal to the pump intensity and the modal group velocities. The formalism is then applied to two prospective schemes for enhanced stimulated Raman generation in slow-light photonic crystal waveguides. The results demonstrate a maximum factor of 10^4 (66,000) enhancement with respect to SOI channel waveguides. Effects of two photon absorption, intrinsic scattering, and disorder with respect to slow-light Raman generation towards optically-pumped silicon amplifiers and lasers are also discussed.

physics.optics↗

arXiv2005

Demonstration of Near-Infrared Negative-Index Materials

Metal-based negative refractive index materials have been extensively studied in the microwave region. However, negative-index metamaterials have not been realized at near-IR or visible fre-quencies due to difficulties of fabrication and to the generally poorer optical properties of metals at these wavelengths. In this paper, we report the first fabrication and experimental verification of a transversely structured metal-dielectric-metal multilayer exhibiting a negative refractive in-dex around 2 mm. Both the amplitude and the phase of the transmission and reflection were measured experimentally, and are in good agreement with a rigorous coupled wave analysis.

physics.optics↗