Surface-induced photorefractivity in twistable nematics: toward the all-optical control of gain.

We report the first two-beam coupling investigation of the surface-induced photorefractive effect (SIPRE) in optically twistable nematic liquid crystal cell. The unique space-charge field of SIPRE is exploited to achieve optical tuning of the photorefractive gain. A reconfigurable photoaligning substrate is used to adjust the twist angle, which is proved to be a control parameter for the photorefractive gain. The amplitude of the optical modulation increases gradually with the twist. Its phase shift changes from 0 degrees to 90 degrees with the polarization state of the two interfering beams. These results pave the way to the all-optical control of the photorefractive gain

Electrically tunable two-dimensional liquid crystals gratings induced by polarization holography

Two-dimensional (2D) gratings made up of an array of differently twisted nematic structures are obtained by crossed assembling of 1D polarization holograms recorded at the photoaligning substrates. The rotating linear polarization pattern, produced by the interference of two opposite circularly polarized beams, is recorded on the azo-dye doped polyimide aligning layers. The 2D gratings diffract light in different directions with different polarization states, that can be optically controlled. Orthogonal circularly and linearly polarized diffraction orders are simultaneously obtained irradiating the grating with a linearly polarized beam. An external ac voltage allows to completely control the diffracted energy distribution. (c) 2007 Optical Society of Americ

Fonti antiche sui fiumi. Il racconto multimediale nel Museo Consentia Itinera tra ricerca scientifica e nuove forme di comunicazione e divulgazione / Ancient sources on the rivers. The multimedia story in the Museum Consentia Itinera between scientific research and new forms of communication and dissemination

Il saggio intende chiarire il valore della tecnologia digitale applicata in ambito museale nel trasferimento e nella comunicazione dei contenuti scientifici rivolti alla collettività, pur nella varietà dei pubblici, attraverso il caso di studio del Museo multimediale Consentia Itinera, istituito dalla Fondazione Attilio ed Elena Giuliani nel novembre 2017. Basato sulla letteratura su fiumi e culture fluviali studiata per la realizzazione di alcune sale immersive del museo, il testo procede lungo tre direzioni: dapprima viene proposta una rilettura sintetica delle fonti antiche sul fiume Krathis che è stato celebrato nei versi di Eliano, Strabone, Euripide e Ovidio e che è protagonista dello storytelling in Consentia Itinera nonché in numerose opere degli artisti  protagonisti  delle  Residenze  Artistiche  BoCS  Art  ideate  dal Comune di Cosenza dal 2015; in secondo luogo si cerca di chiarire come il museo multimediale restituisca le fonti antiche alla comunità nel rispetto del rigore metodologico e della coerenza scientifica e, infine, si evidenzia l’importante plus valore scientifico e divulgativo seguito dal Museo Consentia Itinera con una pratica museale permanente. Nel testo si cerca inoltre di esporre le nuove competenze scientifiche ed emotive che il museo offre al pubblico con varie soluzioni tecnologiche.This essay want to clarify the value of digital technologies in the museums for the promotion and communication of thescientific research to the communities. As a case study the Multimedial Museum Consentia Itinera founded in November 2017 thanks to Attilio and Elena Giuliani Foundation, in Cosenza. The work will proceed in three directions and  it is based on literature about rivers and rivers cultures studied for the realization of this museum. In the first paragraph we propose a syntheticrereading of the ancients sources about the river Krathis which was celebrated in famous verses of Eliano, Strabone, Euripide andOvidio and which is the protagonist of the artworks of the artists living in Cosenza, during the Artistic Residences BoCS Art from 2015. Secondly we try to explane how Consentia Itinera returns the ancients sources to the community while respectingmethodological rigor and scientific coherence. At the end, we conclude highlighting the important “plus valore” both scientific and popular followed by the Museum Consentia Itinera with a permanent museum practice. In the text we try to exhibit the newscientific and emotional skills that the Museum offers to the publics with various technological solutions.

Polarization gradient: exploring an original route for optical trapping and manipulation.

We report a study of the capabilities of an optical tweezer based on polarization gradient. We use a light polarization pattern that is able to simultaneously exert forces and torques in opposite directions depending on the particle's position. It allows to perform oscillatory displacements and control the sense of rotation of several particles inside a uniformly illuminated region. Unconventional trapping of spinning particles in circularly polarized fringes has been observed, which suggests the involvement of hydrodynamic forces

Polarization holograms allow highly efficient generation of complex light beams

We report a viable method to generate complex beams, such as the non-diffracting Bessel and Weber beams, which relies on the encoding of amplitude information, in addition to phase and polarization, using polarization holography. The holograms are recorded in polarization sensitive films by the interference of a reference plane wave with a tailored complex beam, having orthogonal circular polarizations. The high efficiency, the intrinsic achromaticity and the simplicity of use of the polarization holograms make them competitive with respect to existing methods and attractive for several applications. Theoretical analysis, based on the Jones formalism, and experimental results are shown

Liquid crystal as laser medium with tunable gain spectra.

Amplified spontaneous emission intensity and gain spectra in polarized light have been measured in a dye doped nematic liquid crystal for different orientation of its optical axis and pump intensity. A possibility for switching the gain of the liquid crystal by an external electric field is shown experimentally. The liquid crystal materials with field controlled gain can be used in microlasers and light micro-amplifiers in both planar and waveguiding geometry. (C) 2008 Optical Society of America

Correction: Collective motion of chiral Brownian particles controlled by a circularly-polarized laser beam

Correction for 'Collective motion of chiral Brownian particles controlled by a circularly-polarized laser beam' by Raúl Josué Hernández et al., Soft Matter, 2020, 16, 7704–7714, DOI: 10.1039/C9SM02404B

Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.Comment: 8 pages, 7 figures, LaTeX, accepted to Phys. Rev.