1. Colleen Downs Stephanie Pietromonaco Sanjay Talluri
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

4. 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

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
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 ˚F (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