1,720,998 research outputs found
Multi-wavelength Analysis of Synthetic Tissue Samples by Optical Feedback Interferometry
Full text linkScanless optical feedback imaging principle by single-pixel compressed sensing
No full textOptical feedback in lasers is being used for unconventional imaging of fluid dynamics, pressure fields, material properties, and free-carrier distribution, especially in spectral regions where two-dimensional detectors are not yet available. As this technique requires scanning the laser spot across the target, the resulting image contrast is often hampered by the speckle effect. Compressed sensing is becoming a workhorse technique for signal analysis, allowing the reconstruction of complex images from a relatively small number of integrated (single-pixel) measurements, and is being efficiently adapted to a number of single-pixel detector cameras. We applied compressed sensing algorithms to the inherently single-pixel optical feedback in a semiconductor diode laser, demonstrating for the first time, to the best of our knowledge, scanless and detectorless speckle-free imaging of a simple binary object
DISPERSION OF THE TWO-PHOTON ABSORPTION COEFFICIENT IN ZnSe
No full textThe dispersion of the degenerate two-photon absorption coefficient is measured in ZnSe in the energy region from 2.66 to 3.52 eV, corresponding to 0.5 < hv/E-g < 0.66. Our results clearly show the sizeable contribution of the split-off band to the strength of the nonlinear absorption. By contrasting our measurement with several theoretical calculations, we find that at least the lowest four-bands should be included in the band-structure model of the two-photon absorption. General scaling laws for the calculation of the two-photon absorption coefficient provide a good estimate of the strength of the absorption but fail to account for details of the spectrum
Laser Optical Feedback Turns 60
Full text linkAs soon as a laser is fired, some of the emitted light is scattered backward and coupled with the cavity modes, causing instability. However, already in March 1962, Kleinman and Kisliuk [1] suggested that controlled back reflection from an external mirror could help the stabilization of the fundamental cavity mode by suppressing the higher-order ones. Soon afterward, King and Steward [2] proposed the exploitation of optical feedback for metrology, and laser self-mixing (LSM) eventually became an established research topic. Sixty years and a few thousand publications later, this Special Issue celebrates some of the most recent achievements in optical feedback interferometry (OFI), as LSM is currently addressed.
The Special Issue includes four research articles, each covering one aspect of the multivariate system simply consisting of a laser and a scattering target. These papers relate to modeling new type of lasers, implementing commercial applications, and deepening our understanding of laser dynamics
Self-mixing in multi-transverse mode semiconductor lasers: model and potential application to multi-parametric sensing
Full text linkA general model is proposed for a Vertical Cavity Surface Emitting Laser (VCSEL) with medium aspect ratio whose field profile can be described by a limited set of Gauss-Laguerre modes. The model is adapted to self-mixing schemes by supposing that the output beam is reinjected into the laser cavity by an external target mirror. We show that the self-mixing interferometric signal exhibits features peculiar of the spatial distribution of the emitted field and the target-reflected field and we suggest an applicative scheme that could be exploited for experimental displacement measurements. In particular, regimes of transverse mode-locking are found, where we propose an operational scheme for a sensor that can be used to simultaneously measure independent components of the target displacement like target translations along the optical axis (longitudinal axis) and target rotations in a plane orthogonal to the optical axis (transverse plane). (C) 2012 Optical Society of Americ
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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