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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Long range surface plasmon resonance with ultra-high penetration depth for self-referenced sensing and ultra-low detection limit using diverging beam approach

Using an insulator-metal-insulator structure with dielectric having refractive index (RI) larger than the analyte, long range surface plasmon (SP) resonance exhibiting ultra-high penetration depth is demonstrated for sensing applications of large bioentities at wavelengths in the visible range. Based on the diverging beam approach in Kretschmann-Raether configuration, one of the SP resonances is shown to shift in response to changes in the analyte RI while the other is fixed; thus, it can be used as a built in reference. The combination of the high sensitivity, high penetration depth and self-reference using the diverging beam approach in which a dark line is detected of the high sensitivity, high penetration depth, self-reference, and the diverging beam approach in which a dark line is detected using large number of camera pixels with a smart algorithm for sub-pixel resolution, a sensor with ultra-low detection limit is demonstrated suitable for large bioentities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Surface plasmon resonance induced Er{sup 3+} photoluminescence enhancement in tellurite glass

The melt quenching method is used to prepare tellurite glasses co-activated with erbium ions and silver nanoparticles (Ag NPs). The glass samples are characterized by x-ray diffraction, UV-vis-NIR absorption, transmission electron microscopy (TEM) imaging, and photoluminescence spectroscopy. The XRD pattern shows no sharp peak indicating an amorphous nature of the glasses. The presence of Ag NPs is confirmed from TEM micrograph. The absorption spectra reveal not only the peaks due to Er{sup 3+} ions, but also the surface plasmon resonance band of silver NPs in the 510–535 nm range. The J-O model has been applied to the room temperature absorption intensities of Er{sup 3+} (4f{sup 11}) transitions to establish the so-called J-O intensity parameters: Ω{sub 2}, Ω{sub 4}, and Ω{sub 6}. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) and branching ratios of the Er{sup 3+} transitions from the excited state J manifolds to the lower-lying J' manifolds. Intensified of 1.53 μm band is obtained for the sample containing 0.5 mol. % of AgNO{sub 3} (Ag0.5 glass) using for excitation a laser operating at 980 nm. The simultaneous influence of the Ag NPs → Er{sup 3+} energy transfer and the contribution of the intensified local field effect due to the silver NPs give origin to the enhancement of both the Photoluminescence (PL) intensity and the PL lifetime relative to the {sup 4}I{sub 13/2} → {sup 4}I{sub 15/2} transition, whereas the quenching is ascribed to the energy transfer from Er{sup 3+} ions to silver NPs. Based on the analysis of the temperature dependence of the PL intensity and decay time, we identified a weak back transfer process from Er to the glass host that makes the quenching of the PL intensity weak. Large magnitudes of calculated emission cross-section (σ{sub e}), effective bandwidth (Δλ{sub eff}), and bandwidth quality factor (FWHM × σ{sub e}) relatives to {sup 4}I{sub 13/2} → {sup 4}I{sub 15/2} transition in Er doped Ag0.5 glass have been shown. They indicate that this glass sample has good prospect as a gain medium applied for 1.53 μm band broad and high-gain erbium-doped fiber amplifiers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Transformation of surface plasmon polaritons to radiation in graphene in terahertz regime

We demonstrate a concept that allows direct excitation of surface plasmon polaritons (SPPs) by a moving electron bunch above a single layer graphene sheet deposited on a dielectric substrate without any additional coupling requirements. We show that if the two-dimensional current in the graphene is dominated by the third order nonlinear effect when the surface electric field exceeds a moderate strength of ∼5 kV/cm, the SPP mode can cross the light line although the group velocity remains much smaller than the speed of light. This effect gives rise to direct transformation of SPPs into radiation. The underlying mechanism of the crossing of the SPP dispersion into the light line is the energy shift of charged particles in the nonlinear regime and the finite transport scattering time in graphene. Both the energy and lifetime of the SPPs increase with the field intensity. The radiation intensity and frequency can be tuned with an AC bias.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A new time dependent density functional algorithm for large systems and plasmons in metal clusters

A new algorithm to solve the Time Dependent Density Functional Theory (TDDFT) equations in the space of the density fitting auxiliary basis set has been developed and implemented. The method extracts the spectrum from the imaginary part of the polarizability at any given photon energy, avoiding the bottleneck of Davidson diagonalization. The original idea which made the present scheme very efficient consists in the simplification of the double sum over occupied-virtual pairs in the definition of the dielectric susceptibility, allowing an easy calculation of such matrix as a linear combination of constant matrices with photon energy dependent coefficients. The method has been applied to very different systems in nature and size (from H{sub 2} to [Au{sub 147}]{sup −}). In all cases, the maximum deviations found for the excitation energies with respect to the Amsterdam density functional code are below 0.2 eV. The new algorithm has the merit not only to calculate the spectrum at whichever photon energy but also to allow a deep analysis of the results, in terms of transition contribution maps, Jacob plasmon scaling factor, and induced density analysis, which have been all implemented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Variation in plasmonic (electronic) spectral parameters of Pr (III) and Nd (III) with varied concentration of moderators

It is said that the -4f shells behave as core and are least perturbed by changes around metal ion surrounding. However, there are evidences that-4f shells partially involved in direct moderator interaction. A systematic investigation on the plasmonic (electronic) spectral studies of some Rare Earths[RE(III).Mod] where, RE(III) = Pr(III),Nd(III) and Mod(moderator) = Y(III),La(III),Gd(III) and Lu(III), increased moderator concentration from 0.01 mol dm{sup −3} to 0.025 mol dm{sup −3} keeping the metal ion concentration at 0.01mol dm{sup −3} have been carried out. Variations in oscillator strengths (f), Judd-Ofelt parameters (T{sub λ}),inter-electronic repulsion Racah parameters (δE{sup k}),nephelauxetic ratio (β), radiative parameters (S{sub ED},A{sub T},β{sub R},T{sub R}). The values of oscillator strengths and Judd-Ofelt parameters have been discussed in the light of coordination number of RE(III) metal ions, denticity and basicity of the moderators. The [RE(III).Mod] bonding pattern has been studies in the light of the change in Racah parameters and nephelauxetic ratio.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Design of electric-field assisted surface plasmon resonance system for the detection of heavy metal ions in water

Surface Plasmon Resonance (SPR) sensors are widely used in diverse applications. For detecting heavy metal ions in water, surface functionalization of the metal surface is typically used to adsorb target molecules, where the ionic concentration is detected via a resonance shift (resonance angle, resonance wavelength or intensity). This paper studies the potential of a possible alternative approach that could eliminate the need of using surface functionalization by the application of an external electric field in the flow channel. The exerted electrical force on the ions pushes them against the surface for enhanced adsorption; hence it is referred to as “Electric-Field assisted SPR system”. High system sensitivity is achieved by monitoring the time dynamics of the signal shift. The ion deposition dynamics are discussed using a derived theoretical model based on ion mobility in water. On the application of an appropriate force, the target ions stack onto the sensor surface depending on the ionic concentration of target solution, ion mass, and flow rate. In the experimental part, a broad detection range of target cadmium ions (Cd{sup 2+}) in water from several parts per million (ppm) down to a few parts per billion (ppb) can be detected.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Controlling two plasmon decay instability in intense femtosecond laser driven plasmas

We investigate the onset of the two-plasmon-decay (TPD) instability in intense femtosecond laser-solid interaction. In particular, this instability, originating at the quarter critical electron density surface in the inhomogeneous plasma, is explored for a wide range of laser parameters-energy, pulse duration, and intensity contrast. By varying these laser parameters, we demonstrate ways to excite and control the growth of the TPD process. The pulse duration scan carried out under a constant laser fluence reveals the pulse width dependent nature of TPD growth. The spectral splitting of the TPD induced three-halves harmonic emission is used to infer the electron temperature near the quarter critical density surface. Moreover, by varying the laser contrast over four orders of magnitude, we find that the intensity threshold of three-halves harmonic emission increases by nearly two orders of magnitude. This contrast dependent intensity threshold for the emission of three-halves harmonic can be a useful diagnostic of the laser contrast.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Nonlinear interaction between surface plasmons and ion oscillations in a semi-bounded collisional quantum plasma

In this paper, we have investigated the nonlinear interaction between high-frequency surface plasmons and low-frequency ion oscillations in a semi-bounded collisional quantum plasma. By coupling the nonlinear Schrodinger equation and quantum hydrodynamic model, and taking into account the ponderomotive force, the dispersion equation is obtained. By solving this equation, it is shown that there is a modulational instability in the system, and collisions and quantum forces play significant roles on this instability. The quantum tunneling increases the phase and group velocities of the modulated waves and collisions increase the growth rate of the modulational instability. It is also shown that the effect of quantum forces and collisions is more significant in high modulated wavenumber regions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Interpreting plasmonic response of epitaxial Ag/Si(100) island ensembles

Associating features in the experimentally measured optical response of epitaxial Ag islands grown on Si(100) with the localized surface plasmon resonances (LSPRs) hosted by the Ag islands is challenging due to the variation of the Si dielectric function over the energy range under consideration. However, it is possible to conclusively identify features in the experimental spectra with LSPR modes oscillating both parallel and perpendicular to the epitaxial interface by simulating the optical response. The Abeles matrix method is used to describe the composite layered system and the Ag islands are modeled using the thin island film model developed by Bedeaux and Vlieger. By incorporating island morphology parameters determined by quantitative analysis of electron micrographs, the simulation faithfully reproduces the main features of the experimental spectra. Individually zeroing the dipoles associated with the LSPR modes enables conclusive identification of their contribution to the optical response of the composite system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Terahertz emission from two-plasmon-decay induced transient currents in laser-solid interactions

We have studied the generation of terahertz (THz) radiation via the interaction of intense femtosecond laser pulses with solid targets at a small incidence angle. It is found that preplasma with a moderate density gradient can enhance the emission. We also observe saturation of the THz output with the driving laser energy. We find that THz emission is closely related to the 3/2 harmonics of the driving laser. Particle-in-cell simulations indicate that under the present experimental conditions, the THz emission could be attributed to the transient currents at the plasma-vacuum interface, mainly formed by the two-plasmon-decay instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Femtosecond laser generated gold nanoparticles and their plasmonic properties

The pulsed laser ablation in liquid medium is now commonly used to generate stable colloidal nanoparticles (NPs) in absence of any chemical additives or stabilizer with diverse applications. In this paper, we report generation of gold NPs (Au NPs) by ultra-short laser pulses. Femtosecond (fs) laser radiation (λ = 800 nm) has been used to ablate a gold target in pure de-ionized water to produce gold colloids with smallsize distribution. The average size of the particles can be further controlled by subjecting to laser-induced post-irradiation providing a versatile physical method of size-selected gold nanoparticles. The optical extinction and morphological dimensions were investigated with UV-Vis spectroscopy and Transmission Electron Microscopy measurements, respectively. Finite difference time domain (FDTD) method is employed to calculate localized surface plasmon (LSPR) wavelength and the near-field generated by Au NPs and their hybrids.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Enhanced plasmon radiative intensity from Ag nanoparticles coupled to a graphene sheet

A hybrid structure composed of Ag nanoparticles and graphene sheets has been synthesized by one-pot co-reduction process at room temperature. Compared to the isolated Ag nanoparticles, the presence of graphene enhanced the photoluminescence originating from the plasmon radiative decay of Ag nanoparticles as results of the charge injection and the near-field confinement resulting from the coupled graphene sheets.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Temperature dependent localized surface plasmon resonance properties of supported gold nanoparticles

The well known localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) supported on a dielectric substrate depends on the particle shape, size and type of dielectric material. The particle size and shape mainly vary with the method of preparation and the parameters involved there in. In this report, we show preparation of AuNPs supported on quartz substrate by direct current sputtering followed by thermal annealing at an optimized temperature of 400 °C. The samples were characterized using optical absorption spectra, scanning electron microscopy (SEM) and the energy dispersive x-ray spectrum. The LSPR position could be tuned by varying annealing temperature. The LSPR was found to be blue shifted up to 10 nm with annealing temperature varying from 400 °C to 800 °C. The change in LSPR was ascribed to the morphology of AuNPs over quartz.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Localized surface plasmon polariton resonance in holographically structured Al-doped ZnO

In this paper, we studied the localized surface plasmon polariton (SPP) resonance in hole arrays in transparent conducting aluminum-doped zinc oxide (AZO). CMOS-compatible fabrication process was demonstrated for the AZO devices. The localized SPP resonance was observed and confirmed by electromagnetic simulations. Using a standing wave model, the observed SPP was dominated by the standing-wave resonance along (1,1) direction in square lattices. This research lays the groundwork for a fabrication technique that can contribute to the core technology of future integrated photonics through its extension into tunable conductive materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Analysis on vertical directional couplers with long range surface plasmons for multilayer optical routing

A structure featuring vertical directional coupling of long-range surface plasmon polaritons between strip waveguides at λ = 1.55 μm is investigated with the aim of producing efficient elements that enable optical multilayer routing for 3D photonics. We have introduced a practical computational method to calculate the interaction on the bent part. This method allows us both to assess the importance of the interaction in the bent part and to control it by a suitable choice of the fabrication parameters that helps also to restrain effects due to fabrication issues. The scheme adopted here allows to reduce the insertion losses compared with other planar and multilayer devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Time resolved detection of two-plasmon decay using three-halves harmonic emission on the National Ignition Facility

Supra-thermal (>100 keV) electrons generated by laser plasma interactions can be detrimental to the performance of ignition experiments conducted on the National Ignition Facility (NIF). On a NIF shot, the amount of electrons is estimated by measuring the hard X-rays passing through the hohlraum wall. The primary sources of hot electrons in a hohlraum are Stimulated Raman Scattering (SRS) and two plasmon decay (TPD). While SRS is well diagnosed on the NIF, there has been no diagnosis of TPD. Here we have designed and implemented a new diagnostic to characterize the time history of TPD on the NIF. The instrument provides a time resolved measurement of the 3/2 ω harmonic emission which is indicative of the presence of TPD. We describe the diagnostic setup, calibration, and the preliminary results obtained on NIF hohlraum experiments. Finally, we find evidence of a correlation between measured hard X-rays generated from the hot electron bremsstrahlung and the TPD emission.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Phonon-induced plasmon-exciton coupling changes probed via oscillation-associated spectra

Coherent vibrations detected in optical experiments can offer insights into material properties and electronic interactions, but also yield complex time-dependent optical signatures, especially in hybridized systems. In this work, we conform to techniques from studies on vibrational wave packets in molecules to analyze the optical signatures of coherent acoustic phonons in nanoparticles. This strategy enables us to better understand the implications of energetic changes induced by coherent phonons. Then, we apply this approach to systems that target coherent acoustic phonons as a route to modulate plasmon-exciton coupling and compare the results to theoretical calculations. Taken together, the described approach provides an intuitive, simple means of analyzing future systems and facilitates attempts to utilize, rather than simply observe, nanomaterial phonon modes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Phase control of coherent acoustic phonons in gold bipyramids for optical memory and manipulating plasmon–exciton coupling

Recent efforts have targeted manipulation of nanomaterial vibrational modes in applications such as chemical/mass sensing, optical switching, and phonon-driven photochemistry. While impulsive photoexcitation can generate coherent phonons, multiple excitation pulses offer the prospect of control and manipulation of coherent phonon modes for functions of optical memory and logic. In this work, we use such an approach to inject an arbitrary coherent phonon phase into a colloidal ensemble of highly monodisperse gold bipyramids. We then demonstrate that this technique can be applied to a system that exhibits plasmon-exciton coupling to further manipulate the hybridization of the system. This ability to manipulate acoustic phonons and hybridization can enable optical logic applications of acoustic phonons in addition to optical memory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗