Search results for "absorption."

Ultraviolet optical properties of silica controlled by hydrogen trapping at Ge-related defects

2007

We studied the effects induced by the ultraviolet-laser and -lamp exposure sequences on the twofold coordinated germanium (=Ge{sup {center_dot}}{sup {center_dot}}) and the H(II) center (=Ge{sup {center_dot}}-H) in silica. The H(II) centers, generated after the first laser irradiation stage by the trapping of atomic hydrogen H{sup 0} at the (=Ge{sup {center_dot}}{sup {center_dot}}), are destroyed by the subsequent lamp exposure with efficiency depending on photon energy. The H(II) photodestruction is activated from {approx}4 eV, and its cross section is here quantitatively measured, so giving the absorption profile of this center. Consistent with the observed correlated recovering of (=Ge{su…

Radiation-induced defects in fluorine-doped silica-based optical fibers: Influence of a pre-loading with H2

2009

International audience; We investigated the effects of 10-keV X-ray radiation on the transmission properties of F-doped optical fibers in the 200–850 nm range of wavelengths (1.5–6 eV). We also studied the influence of pre-loading this kind of fibers with hydrogen on its radiation sensitivity. Our results showed that, for our experimental conditions (pre-treatment with H2 several months before irradiation with diffusion of all the H2 out the fiber core and cladding before X-ray exposure), this pre-treatment increases the radiation-induced attenuation in the ultraviolet part (200–300 nm) of the spectrum. A previous H2-loading has no influence at greater wavelengths. The nature of the radiati…

Spectroscopic studies of the origin of the radiation-induced degradation in phosphorous-doped optical fiber and preforms

2010

In this paper, we study the radiation-induced point defects related to the phosphorus element that is commonly used to improve the optical properties of silica-based glasses but is responsible of a dramatic increase in their radiation sensitivity. To this aim, the influence of x-ray irradiation on prototype phosphorus-doped canonical fibers and their related preforms was investigated by in situ radiation induced attenuation (RIA), optical absorption, and electron spin resonance (ESR) spectroscopy. The RIA spectra in the (1.5-5 eV) range, can be explained by the presence of at least three absorption bands induced by radiation exposure. Additionally the X-dose dependence of such bands was stu…

Absorption, fluorescence and EIT processes in the extremely thin cell filled with Rb and buffer gas neon

2008

International audience; Comparison of the absorption and fluorescence in the nanocell (or so called extremely thin cell) filled with pure Rb with another one filled with Rb and Neon gas is provided. The effect of the collapse and revival of Dicke-type narrowing is still observable for thickness L=lambda/2, and lambda, where lambda , is a resonant laser wavelength either 780 nm, or 795 nm (for Rb, D2 or D1 line). For L=  so called velocity selective optical pumping (VSOP) resonance located at the atomic transition is still observable, while the linewidth is increased by 4 times in comparison with that obtained in the pure Rb nanocell. Comparison with the theory is presented. Electromagnetic…

Peculiarities of resonant absorption on D lines of Cs and Rb for atomic vapour layer of order of light wavelength.

2007

Effect of irradiation temperature on the radiation induced attenuation of Ge-doped fibers

2016

International audience; The UV-visible radiation induced attenuation (RIA) was studied in Ge-doped optical fibers, during X-ray (10 keV) irradiations at different temperatures. By comparing the spectra recorded in dissimilarly irradiated samples we evidenced the impact of the irradiation temperature. In details, we highlighted that, from a certain dose, increasing the temperature the RIA decreases for wavelengths lower than 470 nm, whereas at higher wavelengths the RIA depends only on the dose. Such findings suggest that it is possible to distinguish the irradiation temperature by comparing the signal at two different wavelengths. From the microscopic point of view, it appears that the RIA …

Charge-transfer driven by ultrafast spin-transition in a CoFe Prussian blue analogue

2020

Photoinduced charge-transfer is an important process in nature and technology and is responsible for the emergence of exotic functionalities, such as magnetic order for cyanide-bridged bimetallic coordination networks. Despite its broad interest and intensive developments in chemistry and material sciences, the atomic-scale description of the initial photoinduced process, which couples intermetallic charge-transfer and spin transition, has been debated for decades; it has been beyond reach due to its extreme speed. Here we study this process in a prototype cyanide-bridged CoFe system by femtosecond X-ray and optical absorption spectroscopies, enabling the disentanglement of ultrafast electr…

EXO-PLANETARY HIGH-TEMPERATURE HYDROCARBONS BY EMISSION AND ABSORPTION SPECTROSCOPY (e-PYTHEAS PROJECT)

2019

International audience; e-PYTHEAS is a multidisciplinary project which combines theoretical and experimental work with exoplanet modelling applications. It sits on the frontier between molecular physics, theoretical chemistry and astrophysics. It aims at enhancing our understanding of the radiative properties of hot gaseous media to allow for improved analysis and interpretation of the large mass of data available on the thousands of exoplanets and exoplanetary systems known to date. Our approach is to use theoretical research validated by laboratory experiments and to then inject it into models of the atmospheres of the giant gaseous planets in the solar system and other planetary systems.…

Electronic and Magnetic Study of Polycationic Mn-12 Single-Molecule Magnets with a Ground Spin State S=11

2010

International audience; The preparation, magnetic characterization, and X-ray structures of two polycationic Mn-12 single-molecule magnets (Mn12O12(bet)(16)(EtOH)(4)](PF6)(14)center dot 4CH(3)CN center dot H2O (1) and [Mn12O12(bet)(16)(EtOH)(3)(H2O)](PF6)(13)(OH)center dot 6CH(3)CN center dot EtOH center dot H2O (2) (bet = betaine = (CH3)(3)N+-CH2-CO2-) are reported. 1 crystallizes in the centrosymmetric P2/cspace group and presents a (0:2:0:2) arrangement of the EtOH molecules in its structure. 2 crystallizes in the noncentrosymmetric P (4) over bar space group with two distinct Mn-12 polycations, [Mn12O12(bet)(16)(EtOH)(2)(H2O)(2)](14+) (2A) and [Mn12O12(bet)(16)(EtOH)(4)](14+)(2B) per un…

A Study Using X-ray Absorption and Emission Spectroscopy of Dioxygen-Binding Xerogels Incorporating Cyclam Units Complexed with Copper Salts.

2005

X-ray absorption spectroscopy was used to elucidate how hybrid xerogels complexed with CuCl2 could reversibly bind molecular dioxygen. Difference EXAFS analyses at the Cu K-edge suggest that dioxygen could bridge two Cu atoms in a μ-η1:η1 peroxo-like conformation with unequal Cu···O distances. Only the short distance (RCu–O1 = 1.86 ± 0.01 A) was unambiguously determined and looks typical of a CuII site. The Cu···Cu internuclear distances would be rather long: RCu–Cu ≈ 4.0 A (3.9 A) for the oxygenated (oxygen-free) xerogels. Cl K-edge EXAFS spectra revealed the pre-existence in the oxygen-free xerogels of CuI sites with short Cl–Cu bonds (2.11 ± 0.03 A). Pentacoordinate CuII sites with a lon…