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Accueil > Séminaires et conférences > Séminaires, soutenances de thèses et HDR précédents > 2012 > Séminaires 2012 > Le mardi 25 septembre à 10h30

Le mardi 25 septembre à 10h30

Richard Miles ( Robert Porter Patterson Professor, Ph.D. Stanford University (1972), Professor-in-Charge, Applied Physics Group of Mechanical and Aerospace Engineering Department, Princeton University (USA)) - Velocity, Temperature and Species Imaging in Air and in Combustion Environments by Femtosecond Laser Electronic Excitation Tagging (FLEET)

Palaiseau, salle de réunion du CPHT

Femtosecond laser electronic excitation tagging (FLEET) is a new capability which shows great promise for tagging and following lines and patterns in air flows and in combusting environments without requiring seeding. Through a nonlinear interaction the laser excites and dissociates nitrogen molecules, producing nitrogen atoms throughout the high intensity focal zone of the laser. Those atoms recombine into an excited electronic state of molecular nitrogen, which then fluoresces, emitting light in the red and infrared (First Positive Emission). A ten microsecond lifetime for that fluorescence arises from the time it takes the nitrogen atoms to recombine. Since the laser focal zone forms a line in the air, the long lifetime allows a time gated camera to be used to image the displacement of that line, giving a quantitative measure of the velocity profile. The laser simultaneously produces excited nitrogen molecules that emit over a few nanoseconds in the ultraviolet (Second Positive Emission), leading to an ultraviolet spectral signature that reflects the temperature of the gas along the line. The nonlinear interaction also excites all other species in the flow, so the distribution of species along the line can be determined by their spectral emission signatures. Grid patterns can be written and followed for flow field imaging by using multiple laser beams or by reflecting and refocusing the initial laser beam back through the test environment.

Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Exploitant du site : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Pascal Chabert (Directeur)