1,720,992 research outputs found
Broadband enhanced backscattering spectroscopy of strongly scattering media
Full text linkWe report on a new experimental method for enhanced backscattering spectroscopy (EBS) of strongly scattering media over a bandwidth from 530-1000 nm. The instrument consists of a supercontinuum light source and an angle-dependent detection system using a fiber-coupled grating spectrometer. Using a combination of two setups, the backscattered intensity is obtained over a large angular range and using circularly polarized light. We present broadband EBS of a TiO2 powder and of a strongly scattering porous GaP layer. In combination with theoretical model fits, the EBS system yields the optical transport mean free path over the available spectral window
Method for broadband spectroscopy of light transport through opaque scattering media
Full text linkWe present a new broadband technique for the measurement of di®use light transport throughopaque scattering media. Using the spectral correlations introduced by a scattering medium ontoa white-light supercontinuum spectrum, the di®usion constant of light is determined over a widespectral range in the visible and near infrared. Independent broadband measurements of both thetransport mean free path and the di®usion constant are used to calculate the spectral dependenceof the energy velocity in a porous GaP slab. Broadband correlation spectroscopy is found to be anexcellent tool for the characterization of random scattering media
Enhanced light extraction from emitters close to clusters of resonant plasmonic nanoantennas
Full text linkWe perform time-resolved fluorescence spectroscopy on clusters of plasmonic nanoantennas covered with a dye–polymer mixture. Dimer antenna structures were fabricated consisting of two interacting gold nanorods with varying lengths and interparticle separation. By combining four individual antennas into a cluster within a diffraction limited spot size, we can couple out half of the dye molecule fluorescence via antenna plasmons. Two-dimensional confocal fluorescence lifetime scans visualize the spontaneous emission enhancement of the molecular fluorescence around the antenna clusters
Polycrystalline ZnO nanorods for lasing applications
No full textSingle and double mode random lasing were observed in a polycrystalline ZnO nanorod array. The double mode random lasing showed mode competition when the mode spacing was 2.3 nm or below. Structurally, X-ray diffraction measurements confirmed the formation of the polycrystalline phase, and photoluminescence measurements revealed a broad visible peak due to point defects, suggesting enhanced oxygen diffusion due to annealing. Our results suggest polycrystalline nanorods prepared by chemical bath deposition as a material system for obtaining random lasing for optoelectronic applications and devices
Oxide materials for emerging applications in photonics: introduction to the special issue
Full text linkThis is an introduction to the feature issue of Optical Materials Express on Oxide Materials for Emerging Applications in Photonics
Spatial modulation microscopy for real-time imaging of plasmonic nanoparticles and cells
No full textSpatial modulation microscopy (SMM) is a technique originally developed for quantitative spectroscopy of individual nano-objects. Here, a parallel implementation of the SMM technique is demonstrated based on a line detector capable of demodulation at kHz frequencies. The capabilities of the imaging system are shown using an array of plasmonic nanoantennas and dendritic cells incubated with gold nanoparticle
High-amplitude, ultrashort strain solitons in solids
Full text linkIn recent years, pressure pulses of very short (picosecond) time duration have found wide application as a diagnostic tool in the semiconductor industry and in fundamental condensed matter research. Next to their application in the studies of nanometer-sized structures, propagation of these short acoustic pulses over millimeter distances at low temperatures has revealed a new field of picosecond acoustics. It has been shown that, for very short strain pulses, phonon dispersion destroys the internal structure of the coherent wavepacket by pulling apart its different frequency components. However, when strain amplitudes are sufficiently increased, a nonlinear pulse-steepening mechanism emerges, that leads to the formation of shock waves. The combined action of the nonlinear and dispersive effects then results in the formation of stable, highly localized solitary waves.
In this thesis, we study the development of picosecond pressure pulses into trains of ultrashort acoustic solitons in a bulk crystal. The high-amplitude, bipolar strain wavepackets are generated by femtosecond optical excitation of a thin chromium film evaporated onto the crystal, using high-power optical pulses from an amplified Ti:sapphire laser. Propagation over millimeter distances at low temperatures is studied by means of two complementary experimental methods. First, the development of low-frequency, gigahertz strain components is monitored using Brillouin light-scattering. By monitoring the scattered intensity against traveled distance of the packets, we demonstrate the breakup of the initial single-cycle pulse into an ultrashort acoustic soliton train, reaching transient pressures up to tens of kilobars and soliton widths less than 0.5 picoseconds, corresponding to only several nanometers in the crystal. Further, we show that the ultrashort strain solitons interact coherently with local electronic two-level systems at terahertz frequency, in optically excited ruby. The strain-induced electronic population can be monitored using the well-known R1- and R2-luminescence lines of the excited Cr3+ impurity-ions in the ruby crystal. Coherent manipulation, and even amplification, of terahertz strain wavepackets using an electronic two-level medium appears well within reach. Finally, we present a novel picosecond ultrasonics setup based on our low-repetition laser system and demonstrate its operation by determining the initial shape of the acoustic wavepacket in the chromium transducer
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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