Search results for "Alignement"
showing 9 items of 19 documents
La molécule d'éthylène soumise à des impulsions laser femtosecondes : spectroscopie rotationnelle et alignement
2006
Talk given by B. Lavorel
Alignement moléculaire par impulsions laser ultrabrèves : Mesures & Applications
2009
The interaction of an intense ultrashort laser pulse with a molecular sample leads, after the end of the pulse, to molecular alignment at specific time under field-free conditions. This thesis is dedicated to the measurements and applications of this effect. The degree of alignment is determined through the variation of the refractive index induced by the rearrangement of the molecular dipoles. A two-dimensional technique allowing to measure molecular alignment on a single-shot basis is reported in this document. The alignment is then exploited in order to determine physical quantities which are usually difficult to estimate through others methods. The "cross-defocusing technique" has been …
Qauntum control of molecular rotation and of processes in Nuclear Magnetic Resonance
2019
The goal of this thesis is to apply quantum control techniques to manipulate molecular rotation and to enhance the efficiency of processes in Nuclear Magnetic Resonance.These techniques have been used theoretically and experimentally to control the orientation of a symmetric top molecule by means of THz laser fields. This study has been extended to the case of a long interaction distance between the field and the sample. In this case, the molecule cannot be approximated as isolated. We have also shown the extend to which the time evolution of the degree of orientation can be shaped. Optimal control techniques were used to design the THz field which allows to reach the corresponding dynamics…
Can we ascertain that an archeological site contains intentional stellar alignments?
2021
We study the different parameters that support the presence of intentional stellar alignments on an archaeological site. We develop a rigorous criterion to quantify the probability of fortuitous orientation on a starrise or a starset. We show that the magnitude of the considered stars and the precision of the angular measurements are the two preponderant parameters. Our study aims at establishing the basis of reliable methods for archaeoastronomy.
Critical reading of some papers related to the Bibracte basin
2021
Since its discovery in 1987, the monumental basin of Bibracte questions archeologists because of its atypical orientation that was thought not to follow the way on which it lies. We study 4 archeoastronomical papers dealing with the orientation of the short and long axes on the sun rise at winter solstice or on peculiar stars and we discuss the validity of these hypotheses.
ALIGNEMENT UNI ET TRIDIMENSIONNEL DE MOLÉCULES PAR IMPULSION LASER FEMTOSECONDE
2007
This thesis is devoted to the study of the alignment of linear and asymmetric top molecules generated by an intense laser pulse. In the case of short pulses with respect to molecular rotation, periodic alignment appears in field-free conditions after the extinction of the field. We study theoretically and experimentally the effects of intensity, temperature and polarization of the electric field on produced alignment. If the field is linearly polarized, the interaction leads to the alignment of the most polarizable axis of the molecule. If the field is elliptically polarized, the pulse can generate a simultaneous alignment of the three principal axes of inertia of an asymmetric top molecule…
Mesure de l'effet Kerr d'ordre élevé des constituants de l'air
2009
Talk given by V. Loriot
Alignment of linear molecules by short duration laser pulses
2005
Alignment of linear molecules is efficiently induced by strong linearly polarized laser pulses. In the case of short pulses with respect to molecular rotation, periodic alignment appears in field-free conditions after the extinction of the field. This manuscript presents three techniques where the value of allows to quantify alignment without molecular dissociation nor additional alignment. They use a weak time-delayed probe pulse which experiences the optical properties of an aligned sample and shows modification of its characteristics. The first of them measures a depolarization due to the birefringence of the sample. The second one is based on the defocusing produced by the spatial distr…
CRITICAL REVIEW OF THE ARTICLE “DE BIBRACTE À AUGUSTODUNUM : OBSERVATIONS ARCHÉOASTRONOMIQUES”
2022
Were the towns of Bibracte and Augustodunum astronomically oriented? We study in this publication an article published in the Revue Archéologique de l'Est which puts forward the hypothesis that the Gallic town of Bibracte respects, in its main buildings, orientations corresponding to sunrise on the Romanized dates of the Celtic festivals and that the Roman city of Augustodunum is rather oriented, in its urban fabric, on sunrises at the solstice, like other Roman cities. Our study tends to invalidate these hypotheses, by re-examining the reliability of the measurements taken and the chronology of the constructions in relation to the establishment of the Julian calendar.