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Optical Molasses

Optical Molasses

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Optical Molasses

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  1. Optical Molasses Colleen Downs Stephanie Pietromonaco Sanjay Talluri

  2. Definition • Laser cooling technique that cools atoms to temperatures lower than the Doppler limit • Uses 3 pairs of counterpropagating circularly polarized laser beams which intersect where the atoms are present

  3. History • First demonstrated in 1985 by S. Chu • Laser cooling first became popular in 1970’s • This led to the idea of the Doppler limit • Doppler limit – theoretical lowest possible temperature of atoms • Falsified with finding of process of optical molasses

  4. Optical Trapping • Momentum imparted by photons • “light pressure” is the greatest portion of this effect

  5. Optical Molasses vs. Magneto-Optical Trap (MOT) • Both use 3 pairs of counterpropagating laser beams • Trap about the same amount of atoms • Detection of atoms is easier in MOT because of higher density (less spatial extension) • In MOT the magnetic field only acts on atoms as they fall from trap • Optical molasses uses circularly polarized lasers • Optical molasses breaks Doppler limit • In sodium: 40 μK in Optical molasses vs 300 μK in MOT

  6. Current Applications • GPS (Global Positioning System) • Uses time signals from atomic clocks for positioning • Atomic clock – use laser cooling for more precise time signals • Now: use optical molasses for fountain clocks which are even more precise • This leads to better GPS systems

  7. Current Applications • Lene Hau slowed speed of light from 186,282 miles/second to 38 mph • Used a combination of Optical molasses and Bose-Einstein condensate • Results could improve computer, TV, and night vision goggles

  8. Bose-Einstein Condensate • http://www.youtube.com/watch?v=bdzHnApHM9A • Not made til 1995 because didn’t have the appropriate technological “cooking pot” • Needed vacuums hundreds of trillions of times lower than atmospheric pressure and temperatures of -459.7˚F (within a few billionths of degree from absolute zero)

  9. Process of slowing light atoms • Bose-Einstein condensate slows atoms down to 100 mph which can then be trapped in optical molasses • Optical molasses creates a clump of cold atoms • These cold atoms then undergo evaporative cooling • Take out atoms that are still too hot or energetic from the magnetic field

  10. Slowing of light • First laser – shot across cloud of condensate • controls speed of second because of quantum interference • Second laser – shot perpendicular to cloud and interferes with the first • These 2 lasers result in light traveling at 38 mph

  11. Applications of slow light • Improve communication • Reduce electronic noise • Cut power requirements (a million fold!) • Ranges from telephones to super computers • Hau currently trying to reduce speed of light to 1 cm/second