Optical Molasses

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
(No Transcript)
4
History

• First demonstrated in 1985 by S. Chu
• Laser cooling first became popular in 1970s
• 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

5
Optical Trapping

• Momentum imparted by photons
• light pressure is the greatest portion of this
  effect

6
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

7
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

8
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

9
Bose-Einstein Condensate

• http//www.youtube.com/watch?vbdzHnApHM9A
• Not made til 1995 because didnt have the
  appropriate technological cooking pot
• Needed vacuums hundreds of trillions of times
  lower than atmospheric pressure and temperatures
  of -459.7F (within a few billionths of degree
  from absolute zero)

10
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

11
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

12
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