Search results for "Polarization"
showing 10 items of 1884 documents
Surface plasmon assisted thermal coupling of multiple photon energies
2006
A novel optical effect can be observed in a thin gold foil due to the excitation of surface plasmons which permits a form of all-optical modulation at low pulse rates. Modulated excitation of surface plasmons by infrared photons is shown to couple to several beams at visible-photon energies. The coupling is manifested by the observation of the visible photons being pulsed by the action of the infrared pulses, and by the far field diffraction of the visible beams into concentric rings. When each visible beam also excites surface plasmons, then a quadratic dependence of the visible photon power upon the infrared incident power is measured. The decay of surface plasmons is implicated as the pr…
ASSESMENT OF TEMPERATURE POLARIZATION IN MEMBRANE DISTILLATION CHANNELS BY LIQUID CRYSTAL THERMOGRAPHY
2014
AbstractThe measurement of local temperature distributions within a membrane distillation (MD) channel is a crucial step for the optimization of the channel and spacer geometry. This information allows the estimation of temperature polarization phenomena, which can dramatically influence the thermal efficiency of the process and the optimal choice of the geometric configuration (net spacer features, channel size, etc.). In the present work, a recently presented experimental technique, based on the use of thermochromic liquid crystals and digital image analysis, has been employed in order to assess the temperature polarization phenomena. The local heat transfer coefficient distribution on th…
Acyl-Chain Mismatch Driven Superlattice Arrangements in DPPC/DLPC/Cholesterol Bilayers
2010
Fluorescence and infrared spectroscopy and cholesterol oxidase activity were employed to investigate the effect of phosphatidylcholine (PC) acyl chain length mismatch on the lateral organizations of lipids in liquid-ordered dipalmitoyl-PC/dilauroyl-PC/cholesterol (DPPC/DLPC/CHOL) bilayers. Plots of steady-state fluorescence emission anisotropy of diphenylhexatriene (DPH) labeled PC (DPH-PC) embedded in the DPPC/DLPC/CHOL bilayers revealed significant peaks at several DPPC mole fractions (Y(DPPC)) when the cholesterol mole fraction (X(CHOL)) was fixed to particular values. Analogously, the DPH-PC anisotropy peaked at several critical X(CHOL)'s when Y(DPPC) was fixed. Acyl chain C-H and C hor…
Vibrio cholerae cytolysin: assembly and membrane insertion of the oligomeric pore are tightly linked and are not detectably restricted by membrane fl…
2000
AbstractHemolytic strains of Vibrio cholerae secrete a cytolysin that, upon binding as a monomer, forms pentameric pores in animal cell membranes. Pore formation is inhibited at low temperature and in the absence of cholesterol. We here posed the following questions: firstly, can oligomerization be observed in the absence of pore formation? Secondly, is membrane fluidity responsible for the effect of temperature or of cholesterol upon pore formation? The first issue was approached by chemical cross-linking, by electrophoretic heteromer analysis, and by electron microscopy. None of these methods yielded any evidence of a non-lytic pre-pore oligomer. The second question was addressed by the u…
A small HSP, Lo18, interacts with the cell membrane and modulates lipid physical state under heat shock conditions in a lactic acid bacterium
2005
International audience; The small heat shock proteins (sHSP) are characterized by a chaperone activity to prevent irreversible protein denaturation. This study deals with the sHSP Lo18 induced by multiple stresses in Oenococcus oeni, a lactic acid bacterium. Using in situ immunocytochemistry and cellular fractionation experiments, we demonstrated the association of Lo18 with the membrane in O. oeni cells submitted to heat shock. The same result was obtained after exposure of cells to ethanol or benzyl alcohol, agents known to have an influence on membranes. For the different stresses, the protein was located on the periphery of the cell at membrane level and was also found within the cytopl…
Long-lived dynamic heterogeneity in a relaxor ferroelectric
1998
The polydispersive dielectric response of the relaxor ferroelectric lead magnesium niobate was investigated using nonresonant spectral hole-burning experiments. Using large alternating electric fields, specific parts of the relaxation-time distribution could be addressed selectively. This provides evidence for the dynamic heterogeneity of the dipolar reorientation process. The refilling of single as well as of double holes was much slower than the time scale set by the pump frequencies. Upon refilling, the holes exhibited no signs of spectral broadening. The present findings suggest a speedup of polarization response associated with a domain-wall depinning that is induced by the hole-burnin…
Stark level crossing and optical-rf double resonance in NaK D 1 Π
1997
We report here (Lambda) -doubling splitting and permanent electric dipole moment d p measurements for a number of vibrotational levels of NaK D 1 II state. Two different methods, which are not Doppler limited, were used. Stark effect induced level crossing was registered as fluorescence polarization changes with external electric field, which allowed us to obtain, from one fit, the values of electric dipole moment and (Lambda) -doubling splitting (Delta) ef between e, f substates of an individual rotational state. Another method consisted in obtaining the ratio (Delta) ef /d p from electric field dependence of the intensity of forbidden line appeared in fluorescence as a result of e- f Star…
Polarization switchable Erbium-doped all-fiber laser
2008
We report an experimental study of an erbium-doped all-fiber laser with electrically switchable output polarization. Fiber Bragg grating written in a polarization maintaining optical fiber and attached to a piezo-ceramic actuator is used to commute the polarization state of the laser emission. The laser oscillates at one of two orthogonal polarizations depending on voltage applied to the actuator.
Actively Q-switched DFB fiber laser for Brillouin sensor applications
2009
Q-switching of distributed feedback (DFB) fiber lasers permits to achieve high peak powers, preserving an ultra narrow linewidth [1,2]. The development of a new in-line acousto-optic modulator based on a magnetostrictive actuator, instead of a piezoelectric-based device, permits an efficient excitation of elastic pulses propagating along the optical fiber and an easy access to both emission outputs of the laser. The repetition rate can be continuously adjusted, as well as the amplitude of the elastic pulses. The interaction of these elastic pulses with a fiber Bragg grating written in an erbium-doped fiber permits an actively Q-switched operation of the DFB fiber laser [3]. The birefringenc…
Single- to three-wavelength switchable ytterbium-doped fiber laser based on intracavity induced loss by a long-period holey fiber grating
2011
In this paper, we propose and demonstrate a versatile and simple single-, dual- and three-wavelength switchable ytterbium-doped fiber laser using the intracavity induced-loss generated by a mechanically induced long-period grating (MLPFG) in a holey fiber. The laser net gain in the cavity is reshaped through the MLPFG by adjusting the twist rate and the pressure of the holey fiber in the long-period grating. In this way, the twist response of the MLPFG enables the laser to switch between the single-, dual-, and three-wavelength operations and the tuning of the simultaneous two- and three-wavelengths. These results are of great interest in the design of flexible multiwavelength sources with …