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Optical Molasses: A Laser Cooling Revolution

Explore the history, applications, and groundbreaking methods of optical molasses in cooling atoms to incredibly low temperatures. Learn how optical molasses has revolutionized technologies like GPS and slowed the speed of light, paving the way for advanced applications.

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Optical Molasses: A Laser Cooling Revolution

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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

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