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Working Group 4.31

Two-Step Laser Cooling

The temperature, that can be reached with laser cooling methods, depends on the time scale of the cooling process. Slow processes are more sensitive to the atomic motion. They allow to probe the atomic velocity with higher accuracy and to accurately transfer atoms to the lowest velocities. For calcium this can be achieved by using the extremely narrow transition at 657 nm.

Using this method we have cooled a cloud of approximately one million calcium-atoms to a temperature of a few millionth of one centigrad (6 µK) above absolute zero. The average velocity was as low as 5 cm/s.