LASER COOLING AND TRAPPING<br />BY HARISH GOUD PULI<br />17 March 2010<br />University of Arkansas<br />harishfysx@gmail.c...
It all started in 1975<br />1975             Hänsch/Schawlow and Wineland/Dehmelt : possibility of laser cooling<br />1978...
Temperature Scale<br />300K Room temperature<br />30K Resonant  Collisions<br />3K Liquid helium<br />3mK Optical Cooling<...
Atoms in gases<br />Hot gas<br />Atoms at room temperature have velocities ~ 666 m/s<br />Cold gas<br />harishfysx@gmail.c...
Light exerts force<br />harishfysx@gmail.com<br />
Resonance<br />Force<br />Frequency<br />harishfysx@gmail.com<br />
Frequency Mismatch<br />Laser<br />Atomic beam producer(OVEN)<br />harishfysx@gmail.com<br />
Frequency  match<br />Laser<br />Atomic beam producer(OVEN)<br />harishfysx@gmail.com<br />
Doppler shifting of frequency<br />Force<br />Frequency<br />harishfysx@gmail.com<br />
Doppler Effect<br />Atoms moving to left feel strong force<br />Laser<br />Atoms moving to right feel nothing<br />harishf...
Viscous Drag Force<br />Laser<br />Optical Molasses<br />Laser<br />Laser<br />So no matter in what direction atom moves ,...
Magneto Optical Trapping<br />m=+1<br />m=-1 <br />m=0<br />harishfysx@gmail.com<br />
harishfysx@gmail.com<br />
Equilibrium<br /> in this process atom first absorbs photons and then emits it. <br />When atom emits photon it gets kicke...
Doppler Temperature<br />Boltzmann Constant<br />Doppler Temperature Limit<br />Energy width of optical transition.<br />h...
Problems <br />Beam of atoms have huge spread of velocities. All atoms can not be  slowed down. <br />Once the atom slows ...
Zeeman Cooling<br />Magnetic Field Compensates Doppler Shift<br />Atoms stays in resonance with the laser through out its ...
Theory≠Practical<br />Expected Temperature 240 µK<br />Measured Temperature 40 µK<br />harishfysx@gmail.com<br />
SOLUTION<br />Resolution of this problem was published by Dalibard and Cohen-Tannoudji<br />The sources of this additional...
Sisyphus Cooling<br />Superposition of the counter propagating fields gives rise to the position dependent polarization of...
Assume an atom with a doublet ground state<br />Ground state manifold is coupled by the radiation field to the quadruplet ...
Atom in the light field<br />Field  excites <br />transition <br />Field excites <br />transition <br />Further Selection ...
Periodic modulation of atomic levels<br />Since the intensities of the polarization states vary in<br />space, the energy ...
Atom in the light field<br />Consider a point where the field is left circularly polarized<br />The related weights for th...
The net result of this process is pumping of atoms from             into           which has at this location lower energy...
Its movie time<br />harishfysx@gmail.com<br />
Laser cooling : demonstrated species<br />harishfysx@gmail.com<br />
Evaporative cooling<br />harishfysx@gmail.com<br />
Atom Cloud &Temperature Measurement<br />harishfysx@gmail.com<br />
Atom Cloud Measurement<br />CCD  camera<br />atom cloud<br />imaging lenses<br />laser beam<br />UHV glass cell<br />haris...
Temperature measurement<br />harishfysx@gmail.com<br />
Applications<br />For making better atomic clocks<br />High resolution spectroscopic measurements<br />Studying ultra cold...
harishfysx@gmail.com<br />
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Harish laser cooling

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Harish laser cooling

  1. 1. LASER COOLING AND TRAPPING<br />BY HARISH GOUD PULI<br />17 March 2010<br />University of Arkansas<br />harishfysx@gmail.com<br />
  2. 2. It all started in 1975<br />1975 Hänsch/Schawlow and Wineland/Dehmelt : possibility of laser cooling<br />1978 First demonstration of laser cooling for trapped ions (Neuhauser et al.; Wineland et al.)<br />1982 First stopping of a thermal beam (Philips & Metcalf)<br />1985 First cooling of sodium atoms (Chu, Hollberg et al.) --- 240 μK<br />1987 Theory of magneto-optical trap (MOT) (Dalibard et al.)<br />1988 Sub-Doppler cooling (Cohen-Tannoudji et al.)--- 40 nK<br />1995 Laser + evaporative cooling (Anderson, Cornell et al.) --- 20 nK<br />Nobel Prizes<br />1989 Paul ion-trap<br />1997 Chu, Cohen-Tannoudji, Philips laser cooling & trapping<br />2001 Cornell, Ketterle, Wieman BEC<br />2005 Glauber, Hall, Hänsch laser-based precision spectroscopy<br />harishfysx@gmail.com<br />
  3. 3. Temperature Scale<br />300K Room temperature<br />30K Resonant Collisions<br />3K Liquid helium<br />3mK Optical Cooling<br />300µK Doppler Limit<br />3µ K Recoil Limit<br />2nK Evaporative Cooling<br />0K Absolute zero<br />harishfysx@gmail.com<br />
  4. 4. Atoms in gases<br />Hot gas<br />Atoms at room temperature have velocities ~ 666 m/s<br />Cold gas<br />harishfysx@gmail.com<br />
  5. 5. Light exerts force<br />harishfysx@gmail.com<br />
  6. 6. Resonance<br />Force<br />Frequency<br />harishfysx@gmail.com<br />
  7. 7. Frequency Mismatch<br />Laser<br />Atomic beam producer(OVEN)<br />harishfysx@gmail.com<br />
  8. 8. Frequency match<br />Laser<br />Atomic beam producer(OVEN)<br />harishfysx@gmail.com<br />
  9. 9. Doppler shifting of frequency<br />Force<br />Frequency<br />harishfysx@gmail.com<br />
  10. 10. Doppler Effect<br />Atoms moving to left feel strong force<br />Laser<br />Atoms moving to right feel nothing<br />harishfysx@gmail.com<br />
  11. 11. Viscous Drag Force<br />Laser<br />Optical Molasses<br />Laser<br />Laser<br />So no matter in what direction atom moves , it feels the force and cant escape.<br />This situation called Optical Molasses.<br />Laser<br />harishfysx@gmail.com<br />
  12. 12. Magneto Optical Trapping<br />m=+1<br />m=-1 <br />m=0<br />harishfysx@gmail.com<br />
  13. 13. harishfysx@gmail.com<br />
  14. 14. Equilibrium<br /> in this process atom first absorbs photons and then emits it. <br />When atom emits photon it gets kicked . This is heating process<br />So there is competition between heating and cooling process. Finally atoms come to an equilibrium temperature.<br />harishfysx@gmail.com<br />
  15. 15. Doppler Temperature<br />Boltzmann Constant<br />Doppler Temperature Limit<br />Energy width of optical transition.<br />harishfysx@gmail.com<br />
  16. 16. Problems <br />Beam of atoms have huge spread of velocities. All atoms can not be slowed down. <br />Once the atom slows down it cant absorb light any more<br />Andreev,Balykin,Letokhov and Minogin 1981<br />harishfysx@gmail.com<br />
  17. 17. Zeeman Cooling<br />Magnetic Field Compensates Doppler Shift<br />Atoms stays in resonance with the laser through out its journey from one end to another end<br />harishfysx@gmail.com<br />
  18. 18. Theory≠Practical<br />Expected Temperature 240 µK<br />Measured Temperature 40 µK<br />harishfysx@gmail.com<br />
  19. 19. SOLUTION<br />Resolution of this problem was published by Dalibard and Cohen-Tannoudji<br />The sources of this additional cooling is fortuitous combination of multilevel atoms,polrization gradients, light shifts and optical pumping.<br />They named this phenomena as “Sisyphus” cooling<br />harishfysx@gmail.com<br />
  20. 20. Sisyphus Cooling<br />Superposition of the counter propagating fields gives rise to the position dependent polarization of the electric field... polarization gradient.<br />X-Polarized<br />Y-Polarized<br />harishfysx@gmail.com<br />
  21. 21. Assume an atom with a doublet ground state<br />Ground state manifold is coupled by the radiation field to the quadruplet excited state manifold.<br /> Selection Rules<br />harishfysx@gmail.com<br />
  22. 22. Atom in the light field<br />Field excites <br />transition <br />Field excites <br />transition <br />Further Selection Rules<br />1/3<br />1/3<br />Clebsch –Gordan Coefficients<br />1<br />1<br />Absorption<br />harishfysx@gmail.com<br />
  23. 23. Periodic modulation of atomic levels<br />Since the intensities of the polarization states vary in<br />space, the energy shifts are also position dependent.<br />We will get Stark shifts for the ground states as function of sine for states <br />Or function of cosine for state<br />harishfysx@gmail.com<br />
  24. 24. Atom in the light field<br />Consider a point where the field is left circularly polarized<br />The related weights for the transitions are given by Clebsch Gordon Coefficients .<br />From Clebsch Gordon coefficients we can conclude that the excited state with m=1/2 is more likely to decay back to ground state with m=1/2<br />1<br />Squares of Clebsch –Gordan Coefficients<br />2/3<br />1/3<br />harishfysx@gmail.com<br />
  25. 25. The net result of this process is pumping of atoms from into which has at this location lower energy<br /> than <br />Thus atom climbs up these potential hills and it would be put back to bottom of the hill by spontaneous emission. This is effective way of losing kinetic energy<br />harishfysx@gmail.com<br />
  26. 26. Its movie time<br />harishfysx@gmail.com<br />
  27. 27. Laser cooling : demonstrated species<br />harishfysx@gmail.com<br />
  28. 28. Evaporative cooling<br />harishfysx@gmail.com<br />
  29. 29. Atom Cloud &Temperature Measurement<br />harishfysx@gmail.com<br />
  30. 30. Atom Cloud Measurement<br />CCD camera<br />atom cloud<br />imaging lenses<br />laser beam<br />UHV glass cell<br />harishfysx@gmail.com<br />
  31. 31. Temperature measurement<br />harishfysx@gmail.com<br />
  32. 32. Applications<br />For making better atomic clocks<br />High resolution spectroscopic measurements<br />Studying ultra cold gases, ex: BEC<br />Lithography with cold atomic beams to build accurately controlled structures<br />Ultra precise measurements of gravitational fields<br />Navigation, ex: GPS<br />harishfysx@gmail.com<br />
  33. 33. harishfysx@gmail.com<br />

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