Biomedical subjects

R M Osgood

Publications and source records attributed to R M Osgood.

9 recordsLinked to original sources

PubMed2005

Experimental demonstration of near-infrared negative-index metamaterials.

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 frequencies due to difficulties of fabrication and to the generally poor optical properties of metals at these wavelengths. In this Letter, we report the first fabrication and experimental verification of a transversely structured metal-dielectric-metal multilayer exhibiting a negative refractive index around 2 microm. 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.

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PubMed2005

Photoinduced-reaction dynamics of halogenated alkanes on iron oxide surfaces: CH3I on Fe3O4(111)-(2x2).

The adsorption, thermal chemistry, and photoreaction dynamics of methyl iodide on the (2x2) magnetite termination of natural single-crystal hematite have been investigated by time-of-flight quadrupole mass spectrometry (TOF-QMS), temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). The methyl iodide thermal desorption spectra, taken after dosing the (2x2) surface at 100 K with CH(3)I, show a multiple-peak coverage-dependent behavior, consistent with the presence of several distinct adsorbed phases, along with defect-mediated dissociative chemisorption in the first monolayer. At >1 ML, methyl iodide forms a metastable physisorbed second layer, which desorbs at 148 K, but at higher coverage converts to a layer, which desorbs at 170 K. In the presence of low-fluence-pulse irradiation at 248 nm, angle-resolved TOF-QMS measurements show that 1.6 and 0.3 eV CH(3) fragments are ejected from the adsorbate surface; these fragments originate from direct photodissociation and dissociative photoinduced electron transfer, respectively. These energetic photoejected fragments have characteristic angular distributions peaked at approximately 0 degree with respect to the surface normal. These results and the coverage-dependent relative intensities suggest that the predominant orientation in the first monolayer of the adsorbed CH(3)I is normal to the crystal plane.

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PubMed2005

Integrable wide-free-spectral-range Fabry-Perot optical filters using free-standing LiNbO3 thin films.

We demonstrate the use of free-standing thin films of a complex oxide for chip-scale optical filtering. The films are used as low-order etalons with very large free spectral ranges that exceed 6.78 THz (> 50 nm at 1550 nm) and use a small chip area (< 500 microm2) when they are integrated. The films are produced by crystal ion slicing; this process exfoliates a micrometers-thin layer of single-crystal optical material from a bulk parent by means of high-energy-ion implantation. The etalons, which are 10 microm thick with Ag deposited on both surfaces, are integrated into a silica-on-silicon waveguide block.

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PubMed2005

Parametric light bullets supported by quasi-phase-matched quadratically nonlinear crystals.

We present a comprehensive analysis of the dynamics of three-dimensional spatiotemporal nonspinning and spinning solitons in quasi-phased-matched (QPM) gratings. By employing an averaging approach based on perturbation theory, we show that the soliton's stability is strongly affected by the QPM-induced third-order nonlinearity (which is always of a mixed type, with opposite signs in front of the corresponding self-phase and cross-phase modulation terms). We study the dependence of the stability of the spatiotemporal soliton (STS) on its energy, spin, the wave-vector mismatch between the fundamental and second harmonics, and the relative strength of the intrinsic quadratic and QPM-induced cubic nonlinearities. In particular, all the spinning solitons are unstable against fragmentation, while zero-spin STS's have their stability regions on the system's parameter space.

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PubMed2003

Spatial solitons in type II quasiphase-matched slab waveguides.

The existence and dynamics of one-dimensional spatial solitons formed upon propagation in quasiphase-matched gratings, through three-wave parametric interaction, is analyzed. We study the general case in which the grating exhibits a periodic modulation of both the refractive index and the second-order susceptibility. It is demonstrated that for negative effective wave vector mismatch the induced third-order nonlinearities increase the domain of soliton instability. Finally, the dependence of the efficiency of the second harmonic generation process in the soliton regime, on the parameters of the grating, is discussed.

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PubMed2003

Influence of the dispersive properties of metals on the transmission characteristics of left-handed materials.

We study numerically the influence of the frequency dispersion of the dielectric function of metals on the physical properties of negative-refractive-index metamaterials. A numerical analysis is performed using the transfer matrix formalism in conjunction with the finite-difference time-domain method. We analyze the dependence of the transmission and absorption properties of a slab of split-ring-type resonators on the parameters characterizing the frequency dispersion of the metallic dielectric function: plasma frequency and damping frequency. Then, using these transmission and reflection coefficients, we show that the refractive index remains negative near the resonant frequency of the rings, despite the presence of frequency dispersion. We also determine the dependence of the position and width of the band gaps of a slab of such a metamaterial on the material dispersion. Finally, we also discuss the influence of the shape of the split-ring resonators on the transmission and reflection coefficients. The calculations are performed for both two- and three-dimensional structures.

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PubMed2003

Two-dimensional solitons in quasi-phase-matched quadratic crystals.

We study the existence and dynamics of two-dimensional spatial solitons in crystals that exhibit a periodic modulation of both the refractive index and the second-order susceptibility for achieving quasi-phase-matching. Far from resonances between the domain length of the periodic crystal and the diffraction length of the beams, it is demonstrated that the properties of the solitons in this quasi-phase-matched geometry are strongly influenced by the induced third-order nonlinearities. The stability properties of the two-dimensional solitons are analyzed as a function of the total power, the effective wave-vector mismatch between the first and second harmonics, and the relative strength between the induced third-order nonlinearity and the effective second-order nonlinearity. Finally, the formation of two-dimensional solitons from a Gaussian beam excitation is investigated numerically.

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PubMed2003

Nonlinear optical effects in a two-dimensional photonic crystal containing one-dimensional Kerr defects.

The nonlinear optical effects induced by a one-dimensional (1D) line defect, made of Kerr material, in a 2D photonic crystal are studied. Comprehensive ab initio numerical simulations based on the finite-difference time-domain method show efficient third-harmonic generation in a photonic crystal waveguide consisting of the 1D defect line. The relationship between the third harmonic generation process and the nonlinear modal properties of the waveguide is discussed. We investigate optical limiting in such a device, that is, control of the transmitted power as a function of the Kerr-induced variation of the refractive index. Power dependent spectral changes in such a device and its use as a frequency selector are also examined.

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PubMed2001

Surface-reconstruction-switched adsorbate photofragmentation dynamics.

Energy-resolved angular distributions of neutral fragments ejected during photoinduced electron transfer reaction of CH3Br on GaAs(100) exhibit three distinct methyl-radical ejection channels. These undergo marked changes when the termination is switched from the Ga-rich c(8 x 2) to the As-rich c(2 x 8). Our observations are consistent with a strong adsorption-site dependence of the dynamics.

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