1,720,997 research outputs found
Laser cooling of solids to cryogenic temperatures
No full textLaser radiation has been used to cool matter ranging from dilute gases to micromechanical oscillators. In Doppler cooling of gases, the translational energy of atoms is lowered through interaction with a laser field(1,2). Recently, cooling of a high-density gas through collisional redistribution of radiation has been demonstrated(3). In laser cooling of solids, heat is removed through the annihilation of lattice vibrations in the process of anti-Stokes fluorescence(4-6). Since its initial observation in 1995, research(7-15) has led to achieving a temperature of 208 K in ytterbium-doped glass(16). In this Letter, we report laser cooling of ytterbium-doped LiYF(4) crystal to a temperature of similar to 155 K starting from ambient, with a cooling power of 90 mW. This is achieved by making use of the Stark manifold resonance in a crystalline host, and demonstrates the lowest temperature achieved to date without the use of cryogens or mechanical refrigeration. Optical refrigeration has entered the cryogenic regime, surpassing the performance of multi-stage Peltier coolers
Laser cooling of a semiconductor load to 165 K
No full textWe demonstrate cooling of a 2 micron thick GaAs/InGaP double-heterostructure to 165 K from ambient using an all-solid-state optical refrigerator. Cooler is comprised of Yb(3+)-doped YLF crystal, utilizing 3.5 Watts of absorbed power near the E4-E5 Stark manifold transition. (C) 2010 Optical Society of Americ
Influence of other rare earth ions on the optical refrigeration efficiency in Yb:YLF crystals
No full textWe investigated the effect of rare earth impurities on the cooling efficiency of Yb3+:LiYF4 (Yb:YLF). The refrigeration performance of two single crystals, doped with 5%-at. Yb and with identical history but with different amount of contaminations, have been compared by measuring the cooling efficiency curves. Spectroscopic and elemental analyses of the samples have been carried out to identify the contaminants, to quantify their concentrations and to understand their effect on the cooling efficiencies. A model of energy transfer processes between Yb and other rare earth ions is suggested, identifying Erbium and Holmium as elements that produce a detrimental effect on the cooling performance
Self-referenced subcycle metrology of quantum fields
No full textWe propose and analyze a new time-domain method for subcycle metrology of
quantum electric fields using a combination of a 3rd order nonlinear optical
process and homodyne detection with a local oscillator (LO) field. The new
method enables isolation of intrinsically weak quantum noise contribution by
subtraction of the shot noise of the LO on a pulse-by-pulse basis. Together
with the centro-symmetric character of the nonlinearity, our method unlocks
novel opportunities toward terahertz and mid-infrared quantum field
metrologies
Local laser cooling of Yb:YLF to 110 K
No full textMinimum achievable temperature of similar to 110 K is measured in a 5% doped Yb:YLF crystal at lambda = 1020 nm, corresponding to E4-E5 resonance of Stark manifold. This measurement is in excellent agreement with the laser cooling model and was made possible by employing a novel and sensitive implementation of differential luminescence thermometry using balanced photo-detectors. (C) 2011 Optical Society of Americ
Optical refrigeration to 119 K, below National Institute of Standards and Technology cryogenic temperature
No full textWe report on bulk optical refrigeration of Yb:YLF crystal to a temperature of ∼124 K, starting from the ambient. This
is achieved by pumping the E4-E5 Stark multiplet transition at ∼1020 nm. A lower temperature of 119 +/- 1 K
(∼ − 154C) with available cooling power of 18 mW is attained when the temperature of the surrounding crystal
is reduced to 210 K. This result is within only a few degrees of the minimum achievable temperature of our crystal
and signifies the bulk solid-state laser cooling below the National Institute of Standards and Technology (NIST)-
defined cryogenic temperature of 123 K. © 2013 Optical Society of Americ
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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