Thu Apr 20 09:04:14 BST 2006
Phys. Rev. Lett. 96, 140403 (2006)
- Title: Achieving Peak Brightness in an Atom Laser
- Authors: N. P. Robins, C. Figl, S. A. Haine, A. K. Morrison, M. Jeppesen, J. J. Hope, and J. D. Close (Australian National University)
- Abstract: In this Letter we present experimental results and a simple analytic theory on the first continuous (long pulse) Raman atom laser. We analyze the flux and brightness of a generic two state atom laser with an analytic model that shows excellent agreement with our experiments. We show that, for the same source size, the brightness achievable with a Raman atom laser is at least 3 orders of magnitude greater than achievable in any other demonstrated continuously outcoupled atom laser.
- Comment: Most atom lasers use an RF transition to couple between the magnetic trapped and untrapped (output) states. This paper uses a Raman transition, advantage is lower divergence, higher coupling rate -> brightness about 10^3 times greater than RF output coupler. Continuous output coupling is achieved using the Bragg effect, a non-state-changing two-photon transition (see Science 307 p1945 (2005) for example with BECs). Raman coupler provides a momentum kick to the out-coupled atoms, in contrast to the RF coupler (this is reason for lower divergence). "Gravity causes the condenstate to sag by g/\omega^2 away from the minimum of the magnetic field, broadening the frequency resonance."
Phys. Rev. Lett. 96, 143005 (2006)
- Title: Laser Cooling without Repumping: A Magneto-Optical Trap for Erbium Atoms
- Authors: J. J. McClelland and J. L. Hanssen
- Abstract: We report on a novel mechanism that allows for strong laser cooling of atoms that do not have a closed cycling transition. This mechanism is observed in a magneto-optical trap (MOT) for erbium, an atom with a very complex energy level structure with multiple pathways for optical-pumping losses. We observe surprisingly high trap populations of over 10^6 atoms and densities of over 10^11 atoms cm-3, despite the many potential loss channels. A model based on recycling of metastable and ground state atoms held in the quadrupole magnetic field of the trap explains the high trap population, and agrees well with time-dependent measurements of MOT fluorescence. The demonstration of trapping of a rare-earth atom such as erbium opens a wide range of new possibilities for practical applications and fundamental studies with cold atoms.
- Comment: Key idea is that the metastable states in Erbium have a large enough magnetic moment that they are held in the quadrupole trapping region even while they are in a metastable state that doesn't feel the force from the lasers. "Magnetostatic trapping of high-J metastable states". This means that the population of the MOT is determined by the net loss of metastable atoms from the MOT (slow) rather than the rate of decay from the excited state to metastable states (fast). Rate equation model of the equivalent four level system.
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