Salut,
j'aimerais avoir vos lumières sur un bref article dans le dernier Nature http://www.nature.com/nature/journal...l/440879a.html :
Le principe du laser d'extinction de fluorescence, c'est bien qu'il fait de l'émission stimulée comme dans un LASER ?Envoyé par NatureBiological imaging: The diffraction barrier broken
Garth J. Simpson1
Top of page
Abstract
The conventional optical limitations of fluorescence microscopy have been defied, to achieve nanoscale resolution of individual vesicle organelles at the junctions of neuronal cells.
Traditional optical microscopy cannot easily distinguish objects separated by less than about half the wavelength of visible light. For example, measurements of two fluorescent particles closer together than this 'diffraction barrier' generally produce one indistinct, bright blob. In practice, this equates to a maximum resolution corresponding to distances of around 200 nm for biological imaging using visible light. However, Stefan Hell and colleagues have developed a technique that overcomes the diffraction barrier and can resolve objects separated by less than about 40 nm (refs 1,2,3). On page 935 of this issue, Jahn, Hell and colleagues4 use the technique to provide the first in vitro images of the movements of single neuronal vesicles — the membrane-bound, bubble-like organelles that mediate communication between neurons. Their images help to settle a question that has been exercising cell biologists for some time.
The latest approach uses stimulated emission depletion (STED) microscopy1, 2, 3, a technique that relies on the overlap of two light beams in the focal region. The first beam excites molecules just as in traditional fluorescence microscopy — as the molecule absorbs the energy from the light, it is promoted up to a higher energetic state, and as it relaxes back to the ground state, it releases the energy in the form of light. The second beam, at a different wavelength, suppresses this fluorescence by 'stimulated emission', in which molecules are actively pumped down out of the excited state by light (in essence, absorption driven backwards). In sufficiently intense optical fields, stimulated emission becomes more efficient than fluorescence and is the dominant effect, drastically reducing the fluorescence.
-----