1 Atom lasers and optical lasers

There is a close analogy between an optical laser and an atom laser. An optical laser emits coherent electromagnetic waves, while an atom laser emits coherent matter waves. (a) In an optical laser most of the photons occupy just one or a few of the modes in the laser cavity. This cavity is typically formed by two mirrors (blue), and the modes of the laser are essentially wavelengths defined by the round-trip time of light inside the cavity. Only one mode is shown in the figure. The "gain" medium is pumped by an external source of energy to ensure that large numbers of photons are emitted into that mode. One of the mirrors is usually partially transmitting to allow photons to "leak" out of the cavity, forming a beam of coherent light (green). (b) In an atom laser, a Bose­Einstein condensate in a magnetic trap (blue) contains many atoms in a single state, the lowest-energy state of the trap. The gain medium is a thermal cloud of atoms. The atoms can be extracted from the trap by allowing them to tunnel through the confining potential. The extracted atoms form a beam of coherent matter waves (green).

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