Laser cooling to create a miniature atomic clock

Résumé du document

An atomic clock is one which provides the most accurate definition of the second, and is thus the most important one that exist on Earth. It symbolizes universal time. A tender was launched in 2007 by the European Space Agency (ESA) for the development of a miniature atomic clock in embedded systems (first of all for the satellites and after that for the public), with low energy consumption. The project, funded at a half-million, was begun in October 2007 and could allow some new applications for these ultra accurate clocks. Three laboratories of the Institute for micro technology at the University of Neuchatel won the project and are therefore responsible for this achievement. You should know that a first prototype of such a clock was made in 2004 with the project HORACE. A part of this clock, that helps to reduce the weight and size of the system, is the use of laser cooling atoms of Cesium 133, of which I am going to introduce the principle.

Extraits

[...] Laser cooling to create a miniature atomic clock The atomic clock is the clock which provides the most accurate definition of the second, so it is the one which is the most important that exist on Earth, symbolising universal time. In order to develop this type of clock in embedded systems (first of all for the satellites and after that for the public), a tender was launched in 2007 by the European Space Agency (ESA) on the development of an atomic clock miniature with low energy consuming. [...]

[...] So, to cool an atom, we have to decrease the agitation. At a limit, an atom to which the energy of agitation would be the lowest possible would be at absolute zero. However, this is impossible realize because of the fact that we have got to have an infinite energy. When submitting an atom to a resonant laser radiation, it absorbs a photon, thus gaining the quantity of movement it. It is therefore simply an exchange between the atom and the photon, which will result in a decrease of speed of the atom in the direction of wave propagation. [...]

[...] These radiatives forces can be use to slow the atoms of an atomic beam. For example, the isotope of Rubidium 87, whose lifetime of an excited state is 10 ^ seconds. One of his atom remaining at the atomic resonance makes therefore an average of 10 ^ 8 cycles of re-absorbing every second. If we consider that only the absorption occurs, it takes 3 ms to stop such an atom of 1 meter! However, as we have seen, the absorption of a photon is accompanied by the rebroadcast of it, which will also generate a decrease of speed of the atom, but this time in any direction, which will move away the atom to the incident laser beam. [...]

[...] By adjusting well lasers, it is possible that the force suffered by the atom was opposed to speed. It is as if the atom was moving in a viscous atmosphere that especially reduces its speed since it would go faster. Also it was such a system known as "optical molasses." In an optical molasses, the atoms therefore make erratic movements at speeds low but not zero. The theory imposes that the average speed of atoms can't fall below some ten thousand Kelvin. [...]