Search results for "crystals"

Fine tuning of a photonic band-gap with picosecond laser pulses

2008

We report on light-driven tuning of the optical properties of colloidal photonic crystals (polystyrene opals) doped with gold nanoparticles (Au-np). Using picosecond pulses at 532 nm we obtained permanent changes in the stop band around 1700 nm, with resonance blue shifts as large as 30 nm.

Analysis of multiple internal reflections in a parallel aligned liquid crystal on silicon SLM

2014

Multiple internal reflection effects on the optical modulation of a commercial reflective parallel-aligned liquid-crystal on silicon (PAL-LCoS) spatial light modulator (SLM) are analyzed. The display is illuminated with different wavelengths and different angles of incidence. Non-negligible Fabry-Perot (FP) effect is observed due to the sandwiched LC layer structure. A simplified physical model that quantitatively accounts for the observed phenomena is proposed. It is shown how the expected pure phase modulation response is substantially modified in the following aspects: 1) a coupled amplitude modulation, 2) a non-linear behavior of the phase modulation, 3) some amount of unmodulated light…

The application of the photoacoustic transmittance oscillations for determining elastic constants in gallium and indium selenides

1996

Transmittance periodic oscillations are observed in GaSe and InSe on excitation with optical pulses. Such oscillations are explained in terms of photoacoustic generation of dilatational waves, which become resonant within the crystal. Spectral analysis of those oscillations in samples of different thickness has led to an accurate determination of the longitudinal acoustic‐wave velocity along the crystallographic axis c. Julio.Pellicer@uv.es ; Chantal.Ferrer@uv.es ; Vicente.Munoz@uv.es

Synthesis of Fluorinated Bent-Core Mesogens (BCMs) Containing the 1,2,4-Oxadiazole Ring

2015

New fluorinated bent-core mesogens containing the 1,2,4-oxadiazole or 1,2,4-triazole nucleus have been synthesized taking advantage of the ANRORC (Addition of Nucleophile, Ring-Opening, Ring-Closure) reactivity of 5-perfluoroalkyl-1,2,4-oxadiazoles. Physical state changes of the obtained compounds were characterized through DSC, POM, and SAXS. Besides the formation of a smectic mesophase, a novel behavior as organic molecular glass was evidenced for some 1,2,4-oxadiazole derivatives.

Sintesi di nuovi bent-core LC fluorurati

2011

Parametric Solitons in Two-Dimensional Lattices of Purely Nonlinear Origin

2008

We demonstrate spatial solitons via twin-beam second-harmonic generation in hexagonal lattices realized by poling lithium niobate planar waveguides. These simultons can be steered by acting on power, direction, and wavelength of the fundamental frequency input.

Progress towards the first measurement of charm baryon dipole moments

2021

Electromagnetic dipole moments of short-lived particles are sensitive to physics within and beyond the Standard Model of particle physics but have not been accessible experimentally to date. To perform such measurements it has been proposed to exploit the spin precession of channeled particles in bent crystals at the LHC. Progress that enables the first measurement of charm baryon dipole moments is reported. In particular, the design and characterization on beam of silicon and germanium bent crystal prototypes, the optimization of the experimental setup, and advanced analysis techniques are discussed. Sensitivity studies show that first measurements of $\Lambda_c^+$ and $\Xi_c^+$ baryon dip…

Luminescence and photo-thermally stimulated defect creation processes inPbWO4:Mo,La,Y (PWO III) crystals

2015

Photoluminescence, thermally stimulated luminescence and electron spin resonance are studied for a PbWO4 crystal grown by the Czochralski method at Bogoroditsk Technical Chemical Plant, Russia from the melt with a precise tuning of the stoichiometry and co-doped with La3+, Y3+, and Mo6+ ions. Photo-thermally stimulated processes of electron and hole centers creation under selective UV irradiation of the crystal in the 3.5–5.0 eV energy range and 85–205 K temperature range are clarified and the optically created electron and hole centers are identified. The electrons in this crystal are found to be mainly trapped at the (MoO4)2− groups as well as at the (WO4)2– groups located close to single…

Synthesis and characterization of new azoles as building blocks for functional ionic systems

2015

Zero permeability and zero permittivity band gaps in 1D metamaterial photonic crystals

2007

We consider layered heterostructures combining ordinary positive index materials and dispersive metamaterials. We show that these structures can exhibit a new type of photonic gap around frequencies where either the magnetic permeability \mu or the electric permittivity \epsilon of the metamaterial is zero. Although the interface of a semi-infinite medium with zero refractive index (a condition attained either when \mu= 0 or when \epsilon= 0) is known to give full reflectivity for all incident polarizations, here we show that a gap corresponding to \mu = 0 occurs only for TE polarized waves, whereas a gap corresponding to \epsilon = 0 occurs only for TM polarized waves. These band gaps are …