Search results for "spectroscopie"
showing 10 items of 60 documents
STUDY OF THE INTERNAL DYNAMICS OF NON PLANAR PYRAMIDAL MOLECULES IN VIBRATIONALY VERY EXCITED STATES.
2007
From the U (p+1) formalism, we built a Hamiltonian adapted to the stretching modes of nonplanar XY3 molecules having the C3v group of geometrical invariance. This Hamiltonian is then coupled with two possible Hamiltonians describing the bending modes of these molecular system: a) based on the U (p+1) approach, a bending Hamiltonian is developed and the interaction between the bending and the stretching modes is taking into account through adapted 2:1 resonance coupling operator defined as a Us(4) x Ub(4) enveloping algebra operator ; b) based on the standard normal modes formalism, a bending modes Hamiltonian is expanded and the 2:1 interaction is taken into account as a tensorial product o…
Frequency comb generation by electro-optic modulation and applications
2020
The work presented in this thesis relates the development of a dual frequency comb spectrometer based on the electro-optic modulation of a continuous wave laser, and its utilisation for spectroscopic applications in the near- and mid-infrared.Since their discovery in the 1960s, frequency combs have revolutionised the physics, especially in metrology but also in spectroscopy, which lead to the Nobel Prize in Physics in 2005. In this domain of applications, dual frequency comb spectrometers are known to be complex to develop and use. A possibility to bypass these constraints is to build the spectrometer with electro-optic modulators. This particular architecture makes the experimental setup e…
Controlling rotational dynamics of molecules by shaped ultra-short laser pulses
2004
This manuscript presents various studies falling under the set of themes of coherent control. We establish, as well theoretically as in experiments, the possibility of finely handling the rotational dynamics of linear molecules. In order to operate this handling, the ultra-short pulses are shaped by a pulse shaper. Its principle and its installation are described in a detailed way. The rotational dynamics of the linear nitrogen molecule (N2) is handled while exploiting the relative excitation between the even and odd rotational components of the wavepacket in weak mode of field. That, we chose a periodic phase modulation well defined of the exiting pulse. A temporal analysis comes to clarif…
Study of optical and magneto processes in Rb atomic vapor layer of nanometric thickness
2012
Using a narrow-band resonant fluorescence spectra from a nano-cell with a thickness of L= [lambda]/2, and VSOP resonances formed at a thickness L =[lambda] ([lambda] is the wavelength of the resonant radiation), for the first time it was experimentally investigated the behaviour of the frequency and intensity (transition probabilities) of the atomic hyperfine structure transitions between the 85Rb, 87Rb, D1 and D2 lines Zeeman sublevels in external magnetic fields in range 5 - 7000G. The behaviour of tens of previously unstudied atomic transitions was analyzed and it is demonstrated that the intensities of these lines can both greatly increase, and decrease (tenfold). For the first time it …
Le méthane dans l'atmosphère de Titan. De la spectroscopie fondamentale à la planétologie
2008
Le méthane (CH4) joue sur Tian, le plus gros satellite de Saturne, un rôle similaire à celui de l'eau sur Terre. Il y est de plus à l'origine d'une chimie organique complexe. La spectroscopie étant la technique privilégiée pour mesurer le CH4 dans les atmosphères planétaires, des modèles précis de l'absorption de la lumière par cette molécule doivent être développés. Les résultats récents obtenus dans ce domaine à l'Institut Carnot de Bourgogne, en collaboration étroite avec des planétologues, permettent notamment de contribuer à l'interprétation des résultats de la mission Cassini-Huygens.
Development of direct elemental analysis for process control of nuclear materials manufacturing
2019
In order to optimize the quality control processes of uranium and plutonium metals from nuclear industry production lines, laser-induced breakdown spectroscopy (LIBS) appears as an efficient technique: it enables multi-element, fast and remote chemical analysis that require no sample preparation. Thus, the purpose of our work is to develop this technique towards the quantification of metal impurities in nuclear materials, with an analytical development achieved from surrogate materials. It follows another PhD thesis where a particular spectral band, Vacuum UltraViolet, has been chosen for its performance regarding the detection of several light elements in such materials. However, after per…
Atomic Transitions and Population Control by Laser Frequency Scanning Speed and Magnetic Field
2022
In this thesis the influence of laser radiation and external uniform magnetic field on alkali-metal atomic vapor is studied. We focused on three topics. In the first part, we examined atomic population control in an M-type system to demonstrate that such systems can serve as universal three-bit logical devices. The second part concerns an experiment of atomic spectroscopy. From the fluorescence spectra recorded for stationary, transient and non-stationary interaction regimes, we were able to extract important parameter values which are the relaxation rate of the lower energy levels to the equilibrium isotropic state, the diffusion coefficient in a buffered vapor cell, and the corresponding …
Study of supercontinuum sources based on tellurite glass optical fibers for mid-infrared absorption spectroscopy applied to gas sensing
2015
This work focuses on the development of mid-infrared supercontinuum light sources and their application for gas detection through absorption spectroscopy. The study of supercontinuum sources is based on nonlinear ultrashort pulse propagation in tellurite glass (80TeO2-10ZnO-10Na2O) and used in three different forms, namely a thin bulk sample, a microstructured suspended-core fiber, and a tapered suspended-core fiber. These technical means adapt themselves to distinct laser sources commercially available, thus optimizing the implementation of ultrawide-band infrared light sources. Experimental observations are compared to corresponding numerical simulations, thus pointing out the different u…
Dynamique induite par champ laser femtoseconde intense : alignement moléculaire en milieu gazeux dense et effet Kerr
2011
This thesis is devoted to the study of dynamics induced by intense femtoseconds lasers pulses. The first studied dynamics deals with molecular alignment of CO2-X mixtures (X=CO2, Ar, N2), in dense gases (up to 20 bar). Up to now, this regime has never been studied experimentally. In the field-free regime (after laser/matter interaction), molecular alignment exhibits two components : a permanent alignment and a transient one. The influence of collisions appears through population transfers between rotational states, which leads to a decrease of these two contributions. Permanent alignment relaxation time is only tied to inelastics collisions whereas transient alignment relaxation time is tie…
Determination of fatty acids and lipid classes in salmon oil by near infrared spectroscopy
2017
International audience; Near-infrared (NIR) spectroscopy was evaluated as a rapid method for the determination of oleic, palmitic, linoleic and linolenic acids as well as omega-3, omega-6, and to predict polyunsaturated, monounsaturated and saturated fatty acids, together with triacylglycerides, diglycerides, free fatty acids and ergosterol in salmon oil. To do it, Partial Least Squares (PLS) regression models were applied to correlate NIR spectra with aforementioned fatty acids and lipid classes. Results obtained were validated in front of reference procedures based on high performance thin layer and gas chromatography. PLS-NIR has a good predictive capability with relative root mean squar…