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H. J. Metcalf, P. Straten, Laser Cooling and Trapping

H. J. Metcalf, P. Straten, Laser Cooling and Trapping. Beam deceleration with photon recoil. Absorb a photo to receive momentum kick Spontaneous emission is symmetric Random walk theory assumed Recoil limit. Raman transitions. A two-photon process: a simultaneous absorption

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H. J. Metcalf, P. Straten, Laser Cooling and Trapping

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  1. H. J. Metcalf, P. Straten, Laser Cooling and Trapping

  2. Beam deceleration with photon recoil • Absorb a photo to receive momentum kick • Spontaneous emission is symmetric • Random walk theory assumed • Recoil limit

  3. Raman transitions • A two-photon process: a simultaneous absorption and a stimulated emission by an atom • Two counter-propagating beams • Resonant excitation condition • Linewidth determined by interaction time • At 600nm, pulse duration 0.6ms , equivalent to

  4. Raman cooling J. Foot, Atomic Physics

  5. Experimental demonstration by S. Chu et al. • Using Sodium with hyperfine ground states • Atoms were pre-cooled using beam deceleration magneto-optical trap, and 3D polarization gradient molasses. • Applied a sequence of Raman pulses with controlled linewidth and line shape. • Using Blackman pulse envelope to avoid unwanted off-resonant excitation • Achieve T=100nK, less than 1/10 recoil limit M. Kasevich, S. Chu, Laser cooling below a photon recoil with 3-level atoms, Phys. Rev. Lett. 69, 12 (1992)

  6. Fundamental limit • In theory one can arbitrarily narrow the linewidth • However it takes longer time for narrower linewidth, which limit the Raman cooling in practice.

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