Etoile laser au sodium

[invite91cb62e0]

Bonjour,

Dans plusieurs thèses, il est dit que le laser au sodium est le meilleur choix pour la création d'une étoile laser dans la mesosphère.

Voila ce qu'on me dit :

Section effiace :

Na :
K :
Fe :

Densité surfacique :

Na :
K :
Fe :

Alors il apparait que la densité de Fer est plus importante d'un facteur 2 par rapport au sodium mais que sa section efficace est inférieur d'un facteur 10 environ.

Pourquoi prend-on l'élément qu'il a la plus grande section efficace ?

Merci

Skops :P
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[Gilgamesh]

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[Gilgamesh]

Il manque les unités à ces données.

Sections efficaces :



Source : Lidar: range-resolved optical remote sensing of the atmosphere By Claus Weitkamp

Densités :

Pour le fer :

Iron atom densities in the polar mesosphere from lidar observations

Between March 24 and April 6, 1990, we performed lidar measurements of iron densities above Andøtya, Norway (69° N). In each of the five nights of measurements we observed a regular Fe layer which was confined to the altitude region between 80 and 100 km. Its peak Fe densities occurred at (84.5 ±1) km or approximately 6 km lower than the peak of the sodium layer as observed by us two weeks earlier. The regular Fe layer exhibited column densities of (9 ± 4) ·10⁹ cm^-2 and maximum number densities close to 7,000 cm-3. In addition, sporadic Fe layers were observed frequently between 88 and 108 km, one of which reached a maximum number density of 78,000 cm-3 near 97 km altitude. Properties of the Fe layers as observed by us are compared to those observed by Granier et al. [1989] and by Bills and Gardner [1990].

Pour le sodium :

Lidar observations of substantial sodium depletion in the summertime Arctic mesosphere

The chemistry and dynamics of the mesospheric sodium layer have been studied extensively with lidar (laser radar) techniques since the late 1960s. Meteoric ablation is generally regarded as the dominant source of all mesospheric alkali metals including sodium. The Na layer is typically confined to the region between 80 and 110 km with a peak near the mesopause at 90 km, where the density ranges from 10³ to 10⁴ cm^-3. The Na column abundance at mid-latitudes in the Northern Hemisphere varies from a summer minimum of 3.10⁹ cm^-2 to a winter maximum of 10¹⁰ cm^-2 in December and January

Je vérifie pas pour le Potassium je te fais confiance mais avec tout ça, le produit de la densité surfacique par la section efficace justifie bien le choix du sodium, il me semble. En plus, le doublet de ses raies est très caractéristique.

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