Pierre-and-Marie-Curie University

About: Pierre-and-Marie-Curie University is a education organization based out in Paris, France. It is known for research contribution in the topics: Population & Raman spectroscopy. The organization has 34448 authors who have published 56139 publications receiving 2392398 citations.

Experimental observation of localized optical excitations in random metal-dielectric films

Abstract: Localization of optical excitations within subwavelength areas of a random metal-dielectric film is observed using near-field scanning optical microscopy. This effect is attributed to Anderson localization of surface plasmon modes in a semicontinuous metal film. The localized modes are seen as giant fluctuations of local electric fields spatially concentrated in ``hot'' spots, where the fields are much greater than the applied field. The local near-field spectra consisting of strong resonance peaks are detected and shown to depend markedly on the sample site probed. The observed spectral peaks correspond to localized modes of random metal-dielectric films.

Random quasi-phase-matching in bulk polycrystalline isotropic nonlinear materials.

Abstract: Three-wave mixing in nonlinear materials—the interaction of two light waves to produce a third—is a convenient way of generating new optical frequencies from common laser sources. However, the resulting optical conversion yield is generally poor, because the relative phases of the three interacting waves change continuously as they propagate through the material1. This phenomenon, known as phase mismatch, is a consequence of optical dispersion (wave velocity is frequency dependent), and is responsible for the poor optical conversion potential of isotropic nonlinear materials2. Here we show that exploiting the random motion of the relative phases in highly transparent polycrystalline materials can be an effective strategy for achieving efficient phase matching in isotropic materials. Distinctive features of this ‘random quasi-phase-matching’ approach are a linear dependence of the conversion yield with sample thickness (predicted in ref. 3), the absence of the need for either preferential materials orientation or specific polarization selection rules, and the existence of a wavelength-dependent resonant size for the polycrystalline grains.

Relationships between the prefrontal cortex and the basal ganglia in the rat: physiology of the cortico-nigral circuits.

Abstract: The prelimbic/medial orbital areas (PL/MO) of the rat prefrontal cortex are connected to substantia nigra pars reticulata (SNR) through three main circuits: a direct nucleus accumbens (NAcc)-SNR pathway, an indirect NAcc-SNR pathway involving the ventral pallidum (VP) and the subthalamic nucleus (STN), and a disynaptic cortico-STN-SNR pathway. The present study was undertaken to characterize the effect of PL/MO stimulation on SNR cells and to determine the contribution of these different pathways. The major pattern of responses observed in the SNR was an inhibition preceded by an early excitation and followed or not by a late excitation. The inhibition resulted from the activation of the direct NAcc-SNR pathway because it disappeared after acute blockade of the glutamatergic cortico-striatal transmission by CNQX application into the NAcc. The late excitation resulted from the activation of the indirect NAcc-VP-STN-SNR pathway via a disinhibition of the STN because it disappeared after either CNQX application into the NAcc or blockade of the GABAergic striato-pallidal transmission by bicuculline application into the VP. The early excitation, which was markedly decreased after blockade of the cortico-STN transmission by CNQX application into the STN, resulted from the activation of the disynaptic cortico-STN-SNR pathway. Finally, the blockade of the cortico-STN-VP circuit by CNQX application into STN or VP modified the influence of the trans-striatal circuits on SNR cells. This study suggests that, in the prefrontal cortex-basal ganglia circuits, the trans-subthalamic pathways, by their excitatory effects, participate in the shaping of the inhibitory influence of the direct striato-nigral pathway on SNR neurons.