Search results for "polarization [Upsilon(9460)]"
showing 10 items of 915 documents
Optical Imaging of Coherent Molecular Rotors
2020
International audience; Short laser pulses are widely used for controlling molecular rotational degrees of freedom and inducing molecular alignment, orientation, unidirectional rotation and other types of coherent rotational motion. To follow the ultra-fast rotational dynamics in real time, several techniques for producing molecular movies have been proposed based on the Coulomb explosion of rotating molecules, or recovering molecular orientation from the angular distribution of high-harmonics. The present work offers and demonstrates a novel non-destructive optical method for direct visualization and recording of movies of coherent rotational dynamics in a molecular gas. The technique is b…
Mode cleaning in graphene oxide-doped polymeric whispering gallery mode microresonators
2020
The strategy to incorporate graphene oxide (GO) in a composite material offers significant opportunities to realize compact photonic devices, such as saturable absorbers and polarization selective devices. However, the processing of GO-based composites by direct laser writing, which would afford vast patterning and material flexibility in a single step process, has been little addressed. In this work, we investigated the mechanisms underlying a mode cleaning effect in polymeric whispering gallery mode microresonators containing GO, aiming at the development of on-chip integrable photonic devices. We fabricated the microresonators (cavity loaded Q-factor of 20 000 at 1550 nm) in a single ste…
In-line fiber-optic sensors based on the excitation of surface plasma modes in metal-coated tapered fibers
2001
Abstract Metal-coated tapered fibers are reported as refractive index sensors based on the resonant excitation of surface plasma modes supported by the metal coating. The devices are easy to fabricate and constitute an alternative to metal-coated side-polished fibers and to other sensors made up of bulk components. We report the fabrication and power transmission properties of quasi-circular devices and asymmetric devices. Both sets of devices can be operated as wavelength output sensors, as well as amplitude output sensors. The transmittance of quasi-circular devices is polarization independent and it changes more than 30 dB as a function of external refractive index.
Polarization of SrBi 2 Ta 2 O 9 ceramics at infra‐low frequencies
2009
Dielectric response in the SrBi2Ta2O9 ceramics is studied over a wide range of temperatures at fields up to Emax ≈ 18 kV/cm. Dependence of dielectric permittivity on field intensity is analyzed at different temperatures. A series of polarization loops are obtained at frequencies 0.1 Hz, 1 Hz, and 10 Hz. The hysteresis at switching polarization is displayed by the shape of polarization loops changing with the field amplitude from bi-angles to quasi-saturated loop patterns of a high degree of rectangularity. The ratio of remnant polarization to maximum polarization as function of field amplitude is presented. Thermal behaviour of the coercive field and the half-width of polarization loops is …
k-Space filtering in 2D gradient-echo breath-hold hyperpolarized3He MRI: Spatial resolution and signal-to-noise ratio considerations
2002
In this work some of the factors that can influence the signal-to-noise ratio (SNR) and spatial resolution in MR images of inhaled hyperpolarized gases are systematically addressed. In particular, the effects of RF depletion of longitudinal polarization and image gradient diffusion dephasing were assessed in terms of their contribution to a k-space filter. By means of theoretical simulations and a novel method of experimental validation using a variable transverse magnetization of the 1H signal, systematic quantitative and qualitative investigations of the effects of k-space filtering intrinsic to imaging of hyperpolarized gas were made. A 2D gradient-echo image is considered for a range of…
Nuclear hyperpolarization of 3He by magnetized plasmas
2018
International audience; We describe a method, referred to as PAMP (polarization of atoms in a magnetized plasma), that allowshyperpolarization of 3He nuclear spins at high magnetic field solely by excitation of a rf gas discharge.A magnetized plasma is obtained when the mean free path of the free electrons is much larger than theirgyration radius in the rf gas discharge. Investigations of PAMP are carried out in the 1–15-mbar pressure rangewith rf excitation around 100 MHz. Quantitative NMR measurements at 4.7 T and room temperature showthat, for different cell sizes and gas densities, 3He nuclear polarizations in the 1 to 9% range are achieved(i.e., larger than the Boltzmann equilibrium sp…
Polarization-sensitive hyperspectral imaging of human skin: From system design to clinical validation (Conference Presentation)
2020
We present the development and validation of a new approach for quantitative functional imaging of human skin based on the machine learning technique for the analysis of the hyperspectral skin images. The considered skin parameters include blood volume fraction, blood oxygenation, melanin content, and the epidermal layer thickness. Additionally, the degree of residual polarization of the reflected light has been analyzed. The validity of the approach has been confirmed by the initial preclinical tests with the tissue-mimicking phantoms, functional in-vivo skin tests, and pilot clinical study of type II diabetic patients. The proposed technique has great potential to be implemented in clinic…
Multiexciton complex from extrinsic centers in AlGaAs epilayers on Ge and Si substrates
2013
The multiexciton properties of extrinsic centers from AlGaAs layers on Ge and Si substrates are addressed. The two photon cascade is found both in steady state and in time resolved experiments. Polarization analysis of the photoluminescence provides clearcut attribution to neutral biexciton complexes. Our findings demonstrate the prospect of exploiting extrinsic centers for generating entangled photon pairs on a Si based device. © 2013 AIP Publishing LLC.
Presynaptic nitric oxide/cGMP facilitates glutamate release via hyperpolarization-activated cyclic nucleotide-gated channels in the hippocampus
2011
In hippocampal neurons, synaptic transmission is affected by a variety of modulators, including nitric oxide (NO), which was proposed as a retrograde messenger as long as two decades ago. NO signals via two NO-sensitive guanylyl cyclases (NO-GCs) (NO-GC1 and NO-GC2) and the subsequent increase in cGMP. Lack of long-term potentiation in mice deficient in either one of the two NO-GCs demonstrates the involvement of both NO-GCs in synaptic transmission. However, the physiological consequences of NO/cGMP and the cellular mechanisms involved are unknown. Here, we analyzed glutamatergic synaptic transmission, most likely reflecting glutamate release, in the hippocampal CA1 region of NO-GC knockou…
Femtosecond time resolved coherent anti-Stokes Raman spectroscopy: Experiment and modelization of speed memory effects on H2-N2 mixtures in the colli…
2005
194317; With the aim of temperature diagnostic, femtosecond time-resolved CARS (coherent anti-Stokes Raman spectroscopy) is applied to probe H2 in H2-N2 mixtures. In a first part, a Lorentzian profile is used to model the femtosecond CARS response. A difference between the experimental broadening and the expected one is observed in the collision regime. The observed broadening increases strongly in an inhomogeneous way with respect to the perturber concentration. This is of considerable importance for temperature measurements. In a second part, we show that in the collision regime, this inhomogeneous broadening is due to the speed dependence of the collisional parameters and the memory effe…