Author
Gabriel Gorre
Bio: Gabriel Gorre is an academic researcher from University of Rennes. The author has contributed to research in topics: Polarizer & Depolarizer (optics). The author has an hindex of 1, co-authored 1 publications receiving 40 citations.
Topics: Polarizer, Depolarizer (optics), Iceland spar
Papers
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TL;DR: In this article, the authors demonstrate theoretically and experimentally that using the transparent common Iceland spar as a depolarizer, the Vikings could have performed a precise navigation under different conditions.
Abstract: Viking navigation from Norway to America in the northern latitudes remains a mystery for physicists, historians and archaeologists. Polarimetric methods using absorbing dichroic crystals as polarizers to detect a hidden Sun direction using the polarized skylight have led to controversies. Indeed, these techniques may lack in sensitivity, especially when the degree of polarization is low. Here, we demonstrate theoretically and experimentally that using the transparent common Iceland spar as a depolarizer, the Vikings could have performed a precise navigation under different conditions. Indeed, when simply rotated, such a birefringent crystal can completely depolarize, at the so-called isotropy point, any partially polarized state of light, allowing us to guess the direction of the Sun. By equalizing the intensities of the ordinary and extraordinary beams at the isotropy point, we show that the Sun direction can be determined easily, thanks to a simple sensitive differential two-image observation. A precision of a few degrees could be reached even under dark crepuscular conditions. The exciting recent discovery of such an Iceland spar in the Alderney Elizabethan ship that sank two centuries before the introduction of the polarization of light in optics may support the use of the calcite crystal for navigation purposes.
42 citations
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TL;DR: It is suggested that psychophysical experiments, based upon the perception of polarized light, are amenable to the production of affordable technologies for self-assessment and longitudinal monitoring of visual dysfunctions such as age-related macular degeneration.
Abstract: Like many animals, humans are sensitive to the polarization of light. We can detect the angle of polarization using an entoptic phenomenon called Haidinger's brushes, which is mediated by dichroic carotenoids in the macula lutea. While previous studies have characterized the spectral sensitivity of Haidinger's brushes, other aspects remain unexplored. We developed a novel methodology for presenting gratings in polarization-only contrast at varying degrees of polarization in order to measure the lower limits of human polarized light detection. Participants were, on average, able to perform the task down to a threshold of 56%, with some able to go as low as 23%. This makes humans the most sensitive vertebrate tested to date. Additionally, we quantified a nonlinear relationship between presented and perceived polarization angle when an observer is presented with a rotatable polarized light field. This result confirms a previous theoretical prediction of how uniaxial corneal birefringence impacts the perception of Haidinger's brushes. The rotational dynamics of Haidinger's brushes were then used to calculate corneal retardance. We suggest that psychophysical experiments, based upon the perception of polarized light, are amenable to the production of affordable technologies for self-assessment and longitudinal monitoring of visual dysfunctions such as age-related macular degeneration.
48 citations
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TL;DR: A combined real-time position method based on the use of polarized light and geomagnetic field that works independently of any artificial signal source with no accumulation of errors and can obtain the position and the orientation directly.
Abstract: Many animals exploit polarized light in order to calibrate their magnetic compasses for navigation. For example, some birds are equipped with biological magnetic and celestial compasses enabling them to migrate between the Western and Eastern Hemispheres. The Vikings' ability to derive true direction from polarized light is also widely accepted. However, their amazing navigational capabilities are still not completely clear. Inspired by birds' and Vikings' ancient navigational skills. Here we present a combined real-time position method based on the use of polarized light and geomagnetic field. The new method works independently of any artificial signal source with no accumulation of errors and can obtain the position and the orientation directly. The novel device simply consists of two polarized light sensors, a 3-axis compass and a computer. The field experiments demonstrate device performance.
46 citations
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TL;DR: In this article, a high-pressure synchrotron x-ray diffraction in a diamond anvil cell coupled with direct laser heating of carbon dioxide using a laser was used to identify a crystalline phase of the material above 40 GPa, corresponding to a lower mantle depth of around 1000 km.
Abstract: The stability, structure, and properties of carbonate minerals at lower mantle conditions have significant impact on our understanding of the global carbon cycle and the composition of the interior of the Earth. In recent years there has been significant interest in the behavior of carbonates at lower mantle conditions, specifically in their carbon hybridization, which has relevance for the storage of carbon within the deep mantle. Using high-pressure synchrotron x-ray diffraction in a diamond anvil cell coupled with direct laser heating of ${\mathrm{CaCO}}_{3}$ using a ${\mathrm{CO}}_{2}$ laser, we identify a crystalline phase of the material above 40 GPa---corresponding to a lower mantle depth of around 1000 km---which has first been predicted by ab initio structure predictions. The observed $s{p}^{2}$ carbon hybridized species at 40 GPa is monoclinic with $P{2}_{1}/c$ symmetry and is stable up to 50 GPa, above which it transforms into a structure which cannot be indexed by existing known phases. A combination of ab initio random structure search (AIRSS) and quasiharmonic approximation (QHA) calculations are used to re-explore the relative phase stabilities of the rich phase diagram of ${\mathrm{CaCO}}_{3}$. Nudged elastic band (NEB) calculations are used to investigate the reaction mechanisms between relevant crystal phases of ${\mathrm{CaCO}}_{3}$ and we postulate that the mineral is capable of undergoing $s{p}^{2}\ensuremath{-}s{p}^{3}$ hybridization change purely in the $P{2}_{1}/c$ structure---forgoing the accepted postaragonite $Pmmn$ structure.
32 citations
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25 citations