Evanescent Signal Research Articles

Efficient optical pumping of alkaline atoms for evanescent fields at dielectric-vapor interfaces.

We experimentally demonstrate hyperfine optical pumping of rubidium atoms probed by an evanescent electromagnetic field at a dielectric-vapor interface. This light-atom interaction at the nanoscale is investigated using a right angle prism integrated with a vapor cell and excited by evanescent wave under total internal reflection. An efficient hyperfine optical pumping, leading to almost complete suppression of absorption on the probed evanescent signal, is observed when a pump laser beam is sent at normal incidence to the interface. In contrast, when the pump and probe beams are co-propagating in the integrated prism-vapor cell, no clear evidence of optical pumping is observed. The experimental results are supported by a detailed model based on the optical Bloch equation of a four atomic-level structure, which also includes a treatment of transit relaxation and wall collision with relaxation rates that were obtained directly from the thermal velocities of the atoms and the penetration depth of the evanescent wave. The obtained highly efficient optical pumping at the nanoscale is regarded as an important step in the quest for applications such as optical switching, magnetometry, and quantum memory.

FDTD approach to photonic based angular waveguide for wide range of sensing application

Photonic based angular waveguide is employed in this communication to envisage a wide range of sensing application with the help of finite difference time domain approach, whereproposed photonic structure is realised by 11 × 11 airholes with elimination of series of holes pertaining to L type bending channel, which would be deployed for solving bending loss issues in photonic integrated circuits. However present research is manipulated with visible, infrared signal which acts as input to focus on evanescent signal to comprehend wide range of sensing application, whose ranges from infrared to ultra violet through visible, where the principle of signal is based on the variation of electric field distribution in the said waveguide.

Modes of vertical thermodynamic and wind variability over the Maritime Continent

Abstract. The Maritime Continent (MC) is an exceedingly complex region from the perspective of both its meteorology and its aerosol characteristics. Convection in the MC is ubiquitous and assumes a wide variety of forms under the influence of an evolving large-scale dynamic and thermodynamic context. Understanding the interaction between convective systems and their environment, both individually and in the aggregate, requires knowledge of the dominant patterns of spatial and temporal variability. Ongoing cloud model ensemble studies require realistic perturbations to the atmospheric thermodynamic state to devise system sensitivities. Apart from modeling studies, evanescent signals in the tropical system are obscured by the underlying broad-scale meteorological variability, which if constrained could illuminate fine-scale physical processes. To this end, radiosonde observations from 2008 to 2016 are examined from three upper-air sounding sites within the MC for the purpose of exploring the dominant vertical temperature, humidity, and wind structures in the region. Principal component analysis is applied to the vertical atmospheric column to transform patterns present in radiosonde data into canonical thermodynamic and wind profiles for the MC. Both rotated and non-rotated principal components are considered, and the emerging structure functions reflect the fundamental vertical modes of short-term tropical variability. The results indicate that while there is tremendous spatial and temporal variability across the MC, the primary modes of vertical thermodynamic and wind variability in the region can be represented in a lower-dimensional subspace. In addition, the vertical structures are very similar among different sites around the region, though different structures may manifest more strongly at one location than another. The results indicate that, while different meteorology may be found in various parts of the MC at any given time, the processes themselves are remarkably consistent. The ability to represent this variability using a limited number of structure functions facilitates analysis of covariability between atmospheric structure and convective systems and also enables future systematic model-based ensemble analysis of cloud development, convection, and precipitation over the MC.

Group delay of evanescent signals in a waveguide with barrier

The time history of subsequent tunneled wave packets can represent a more meaningful way to describe signal evolutions and to determine the group delay than the detection of a demodulated monopulse envelope. In the present experimental research, the delay of transmitted tunneled packets was found to be shorter than that measurable in vacuum, in good agreement with the phase time and Esposito's equation and independent of the barrier length. The wave packets did not show narrowing and "reshaping," so these phenomena did not appear to be the reason of the short delay experienced. The latter was not found to be proportional to the amplitude of the incident signal.

Rehabilitating the Importance of the Non-cognitive: An Interview with Michèle Lamont

In spring of 2006, Michèle Lamont, Professor of Sociology and African and African-American Studies at Harvard University, was invited to give a lecture for the New Sociological Imagination Lecture Series, organized by the New School for Social Research. This lecture concerned her book Cream Rising: How Peer Review Finds and Defines Excellence in the Social Sciences and the Humanities, which is to be published by Harvard University Press in 2008. Drawing on 81 interviews with panelists serving on five multidisciplinary fellowship competitions in the social sciences and the humanities, the book analyzes (1) the meaning panelists give to academic excellence—including whether they believe in it or not; (2) how excellence is recognized (both through formal criteria of evaluation, such as originality and significance, but also through more evanescent signals such as the display of cultural capital and the proper use of theory); (3) how excellence is combined with other criteria pertaining to interdisciplinarity and diversity (geographic, institutional, disciplinary, racial, and gender diversity) to push proposals over the proverbial line or to promote or criticize proposals. In her talk, she analyzed the customary rules that panelists say they follow, and which allow them to believe that the evaluation process is fair, and that Cream Rises. In the interview below, we asked her to discuss how procedural fairness actually operates in panels and reflect on many other aspects of the phenomenon that she analyzes.

Readout contrast beyond diffraction limit by a slab of random nanostructures

A simplified Fourier optics approach is applied to study how near-field optical disks retrieve evanescent signals through random nanostructure. The statistical properties of the random nanostructures are used to realize the general behavior of near-field optical disks. The mechanism of its super-resolution capability and an analytical expression of the readout contrast of near-field optical disks with random apertures are derived. The resolution of near-field optical disk is determined by the size of the random nanostructure.

Producing and Editing Diagrams Using Co‐Speech Gesture: Spatializing Nonspatial Relations in Explanations of Kinship in Laos

This article presents a description of two sequences of talk by urban speakers of Lao (a southwestern Tai language spoken in Laos) in which co‐speech gesture plays a central role in explanations of kinship relations and terminology. The speakers spontaneously use hand gestures and gaze to spatially diagram relationships that have no inherent spatial structure. The descriptive sections of the article are prefaced by a discussion of the semiotic complexity of illustrative gestures and gesture diagrams. Gestured signals feature iconic, indexical, and symbolic components, usually in combination, as well as using motion and three‐dimensional space to convey meaning. Such diagrams show temporal persistence and structural integrity despite having been projected in midair by evanescent signals (i.e., handmovements anddirected gaze). Speakers sometimes need or want to revise these spatial representations without destroying their structural integrity. The need to "edit" gesture diagrams involves such techniques as hold‐and‐drag, hold‐and‐work‐with‐free‐hand, reassignment‐of‐old‐chunk‐tonew‐chunk, and move‐body‐into‐new‐space.

Observation of subcellular structures of neurons by an illumination mode near-field optical microscope under an optical feedback control

We propose an illumination mode near-field optical microscope operated under an optical feedback for imaging biological specimens in their natural environment. For feedback control, rapidly varying evanescent signal has been generated over the sample surface. It has been found that evanescent signal can be profitably used as a control signal by utilizing its sample feature dependent discrimination sensitivity. Neurons have been successfully observed both in air and in liquid with a resolution well beyond the diffraction limit.

Fiber-optic fluorimetry in biosensors: comparison between evanescent wave generation and distal-face generation of fluorescent light

A class of continuously working affinity sensors depends on fiber-optic fluorimeters to provide a signal related to analyte concentration. Hitherto, fluorescent light generation at the distal end-face of an optical fiber has been the method of choice. The use of evanescent wave excitation of fluorescence has the potential of improving the response time in such sensors. A direct experimental comparison between the two excitation modes was performed for a particular hard-clad silica fiber at different launching conditions. Furthermore, the background signal from the fiber itself has been investigated. At a launching numerical aperture of 0.6, the evanescent signal from 2–3 cm of decladded fiber equalled that of the end-face configuration in spectroscopic efficiency. The ultimate sensitivity of both methods under their respective optimal conditions were equivalent, with a detection limit of about 10 −8 molar fluorescein.