An atom laser is a coherent state of propagating atoms. They are created out of a Bose-Einstein condensate of atoms that are output coupled using various techniques. Much like an optical laser, an atom laser is a coherent beam that behaves like a wave.
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Introduction
The first pulsed atom laser was demonstrated at MIT by Professor Wolfgang Ketterle et al in November 1996.[1] Ketterle used an isotope of Rubidium and used an oscillating magnetic field as their output coupling technique, letting gravity pull off partial pieces looking much like a dripping faucet (See movie in External Links). From the creation of the first atom laser there has been a surge in the recreation of atom lasers along with different techniques for output coupling and in general research. The current developmental stage of the atom laser is analogous to that of the optical laser during its discovery in the 1960s. To that effect the equipment and techniques are in their earliest developmental phases and still strictly in the domain of research laboratories.
Physics
The physics of an atom laser is similar to that of an optical laser. The main differences between an optical and an atom laser are that atoms interact with themselves, cannot be created as photons can, and possess mass whereas photons do not (they therefore propagate at a speed below that of light).[2] The van der Waals interaction of atoms with surfaces makes it difficult to make the atomic mirrors, typical for conventional lasers. A cw atom laser has not yet been built (source). There are many concepts, which differ in detail, but are basically similar. The condensed atoms are in a crucible, which is held at a temperature, which produces a vapor pressure of about 1 µPa. A glass tube is connected to the crucible. The evaporated atoms fly through this tube. By what is called a 2d-magneto-optical trap, atoms flying almost along the axis of the tube are confined and do not hit the walls, but fly on a sine path. By laser cooling the amplitude of the sine is reduced along the tube. The other atoms change their motion every time they hit the wall and by chance they get into a motion which can be trapped, so as they progress down the tube fewer and fewer atoms hit the walls. It is therefore possible to gradually reduce the temperature of the walls without condensing thick layers of atoms. This collimated beam is sent through a special laser cooling device, a Zeeman slower, so that spread of kinetic energies along the axis is reduced. Evaporative cooling of the transversal motion is possible in a second 2d-magneto-optical trap (source) by pushing back atoms, which reach the border of the trap, by means of an annular shaped laser beam (source). Longitudinal evaporative cooling would be achieved by mixing longitudinal motion in a helical shaped trap or in fountains. Fountains are free atoms flying in parabolas through gravity.
Applications
Atom lasers are critical for atom holography. Similar to conventional holography atom holography uses the diffraction of atoms. The De Broglie wavelength of the atoms is much smaller than the wavelength of light, so atom laser can create much higher resolution holographic images. Atom holography might be used to project complex integrated-circuit patterns, just a few nanometres in scale, onto semiconductors. Another application, which might also benefit from atom lasers, is atom interferometry.In an atom interferometer an atomic wave packet is coherently split into two wave packets that follow different paths before recombining. Atom interferometers, which can be more sensitive than optical interferometers, could be used to test quantum theory, and have so high precision that they may even be able to detect changes in space-time.[3] This is because the de Broglie wavelength of the atoms is smaller than the wavelength of light, the atoms have mass, and because the internal structure of the atom can also be exploited.
See also
References
- ^ MIT (1997) "MIT physicists create first atom laser", http://web.mit.edu/newsoffice/1997/atom-0129.html accessed Jul. 31, 2006.
- ^ MIT's Center for Ultracold Atoms "The Atom Laser", http://cua.mit.edu/ketterle_group/Projects_1997/atomlaser_97/atomlaser_comm.html accessed Jul. 31, 2006.
- ^ Stanford (2003) The Second Orion Workshop "Hyper precision cold atom interferometry in space", http://www-conf.slac.stanford.edu/orion/PAPERS/D02.PDF
