This paper describes the demonstration of an atom laser, emitting coherent atomic beams, using a Bose-Einstein condensate and magnetic trapping. (AIP) {copyright} {ital 1997} Optical Society of America
We demonstrate an atom laser using all-optical techniques. A Bose-Einstein condensate of rubidium atoms is created by direct evaporative cooling in a quasistatic dipole trap realized with a single, tightly focused CO2-laser beam. An applied magnetic field gradient allows the formation of the condensate in a field-insensitive m(F)=0 spin projection only, which suppresses fluctuations of the chemical potential from stray magnetic fields. A collimated and monoenergetic beam of atoms is extracted from the Bose-Einstein condensate by continuously lowering the dipole trapping potential in a controlled way to form a novel type of atom laser.
Since researchers created the first Bose-Einstein condensates (BECs) 3 years ago, they have been eagerly exploring this new state of matter and seeing what can be done with it—turning it into an atom laser, for example (see main text). But the magnetic traps used to confine the condensates put some kinds of studies off limits, because the magnetic fields freeze the spins of the trapped atoms in one orientation. Now Wolfgang Ketterle and his team at the Massachusetts Institute of Technology have removed the barrier with a new kind of trap.
This chapter discusses effective application of low power laser radiations for cooling and use of magnetic field gradient for trapping the atoms. It also discusses the basic principle of operation of Magneto-Optic Traps. Schawlow first showed in the seventies that the optical force of laser radiation can be used to decelerate an atom. This can be accomplished by the absorption of a photon by an atom through a process of stimulated absorption if the laser radiation has a frequency resonant with the energy level difference of the atom. Atoms can be trapped by static magnetic field or a combination of magnetic fields in multipolar, Helmholz or anti-Helmholz configuration or Joffe configuration. Since the atom beams are coherent in nature any beam of atoms from a Bose Einstein condensate can act like an atom laser having high energy that will have very strong penetrating power because of the coherent character of the beam.
Atom lasers have been demonstrated in both pulsed and semi-continuous modes. The dynamics of these devices is predicted to be dramatically different to the optical laser due to fundamental differences between the two types of boson fields, however to date it is the similarities that have been emphasized. Here we show how the atom laser dynamics are strongly affected by coupling of the output beam back to the condensate. Typically research in the field of Bose-Einstein condensation (BEC) 1 relates to studies of fundamental properties, such as collective modes 2 or to the response of the BEC to external stimuli 3. In contrast, the atom laser is one of the most promising technologies to arise from BEC, being the di-rect atomic equivalent of the optical laser 4. Mewes et al. 5 demonstrated the first atom laser, based on the application of pulsed radio-frequency (RF) fields to induce controlled spin flips from magnetically trapped to un-trapped states of a Bose-Einstein condensate. Later it was shown by Hagley et al. 6 that a pulsed Raman out-coupling could be used to achieve a quasi-continuous multi-state atomic beam. Bloch et al. 7 achieved con-tinuous RF out-coulping for up to 100ms, producing a single state atom laser beam, and showed that this beam could be coherently manipulated in direct analogy to the optical laser 8. These experiments, and others 9,10, have conclusively demonstrated that the outcoupling process can be made coherent. They have also demonstrated a number of other similarities be-tween the optical and atomic lasers such as high flux and low divergence of the output beam. In all these works, the similarities between the two sys-tems have been emphasized, however, ultimately it is the differences such as mass and wavelength that will lead to applications of the atom laser. 1