1,721,088 research outputs found
On-Chip Notch Filter on a Silicon Nitride Ring Resonator for Brillouin Spectroscopy
No full textNoncontact Brillouin spectroscopy is a purely optical and label-free method to retrieve fundamental material viscoelastic properties. Recently, the extension to a three-dimensional imaging modality has paved the way to novel exciting opportunities in the biomedical field, yet the detection of the Brillouin spectrum remains challenging as a consequence of the dominant elastic background light that typically overwhelms the inelastic Brillouin peaks. In this Letter, we demonstrate a fully integrated and ultracompact notch filter based on an optical ring resonator fabricated on a silicon nitride platform. Our on-chip ring resonator filter was measured to have a ∼10 dB extinction ratio and a Q factor of ∼1.9 × 105 at 532 nm central wavelength. The experimental results provide a proof-of-concept on the ability of the on-chip filter to attenuate the elastic background light, heralding future developments of fully integrated, ultracompact, and cost-effective Brillouin spectrometers
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
Multi-channel lock-in based differential front-end for broadband Raman spectroscopy
Full text linkIn Broadband Stimulated Raman Spectroscopy, the intrinsic limit given by the laser shot noise is seldom reached due to the electronic noise of the front-end amplifier and the intensity fluctuations of the laser source. In this paper we present a low-noise multi-channel acquisition system, with an integration-oriented design, able to compensate the common-mode fluctuations of the laser output power with the pseudo-differential structure and reach a sensitivity better than 10 ppm thanks to the lock-in technique
Visualizing Coherent Phonon Propagation in the 100 GHz Range: a Broadband Picosecond Acoustics Approach
No full textBuilding on a kHz Ti:sapphire source, we developed a novel pump-probe setup for broadband picosecond acoustics using a white-light continuum probe coupled to an optical multichannel analyser to take snapshots of phonon dynamics. (c
Modular 76-channel instrument for Broadband Raman Spectroscopy
Full text linkRaman microscopy is a label-free and non-invasive technique to reveal the chemical compounds of a sample. However, standard Raman microscopes acquire a single frequency at a time, preventing fast imaging as many biological applications require. Here, we present the preliminary development of a multichannel CMOS-based readout for the simultaneous acquisition of 76 frequencies of the Raman spectrum using the broadband stimulated Raman scattering technique. The acquisition system employs the lock-in technique and a custom multichannel CMOS chip to enable a low-noise operation and a parallel architecture for fast imaging. An FPGA-based DSP chain reduces the low-frequency noise by exploiting a 2-step frequency down-conversion technique. The hardware design of the system based on a motherboard and several module PCBs to realize a highly space-optimized architecture is also presented. Particular emphasis is placed on the experimental results obtained with the 2-step frequency down-conversion technique by means of bench tests
Multichannel Hybrid Lock-In Amplifier for High-Resolution Broadband Raman Spectroscopy
No full textRaman microscopy is a non-invasive and label-free spectroscopic technique with growing applications in the analysis of molecules and biological samples. Fast imaging requires the simultaneous acquisition of multiple wavelengths of the vibrational spectrum with high resolution (approx 10-100ppm). However, the design of a readout capable of combining high resolution and fast acquisition on many channels is still an open challenge. Here, we report a dual-mode, hybrid, multichannel instrument capable of acquiring a Raman spectrum in only 16μ s using analog differential lock-in amplifiers implemented in a custom CMOS chip. For slower measurements, a mixed analog-digital approach can be activated to enhance the signal-to-noise ratio by more than 20dB compared to a fully analog mode. The system can operate in parallel on 76 channels with signals modulated up to 10MHz and an optical power down to 4uW per channel
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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