1. Laser Cooling 1. Doppler Cooling – optical molasses. 2. Magneto-optical trap. 3. Doppler temperature.

2. Doppler Cooling: How can a laser cool? Lab frame v 

3. v  Atom’s frame Doppler Cooling: How can a laser cool?

4. Lab frame v  Atom’s frame Lab frame, after absorption v-v recoil Doppler Cooling: How can a laser cool?

5. Lab frame v  Atom’s frame Lab frame, after absorption v-v recoil Doppler Cooling: How can a laser cool?

6. Lab frame v  Atom’s frame  Absorb a photon  atom gets momentum kick.  Repeat process at 10 7 kicks/s  large deceleration.  Emitted photons are radiated symmetrically  do not affect motion on average  Absorb a photon  atom gets momentum kick.  Repeat process at 10 7 kicks/s  large deceleration.  Emitted photons are radiated symmetrically  do not affect motion on average Lab frame, after absorption v-v recoil Doppler Cooling: How can a laser cool?

7. Lab frame v  Atom’s frame  Absorb a photon  atom gets momentum kick.  Repeat process at 10 7 kicks/s  large deceleration.  Emitted photons are radiated symmetrically  do not affect motion on average  Absorb a photon  atom gets momentum kick.  Repeat process at 10 7 kicks/s  large deceleration.  Emitted photons are radiated symmetrically  do not affect motion on average Lab frame, after absorption v-v recoil m/s m/s 2 87 Rb:  = -  I = I sat V doppler ~ 10 cm/s V recoil = 6 mm/s Doppler Cooling: How can a laser cool?

8. Magneto-Optical Trap (MOT) Problem: Doppler cooling reduces momentum spread of atoms only.  Similar to a damping or friction force (optical molasses).  Does not reduce spatial spread.  Does not confine the atoms.

9. Magneto-Optical Trap (MOT) Solution: Spatially tune the laser-atom detuning with the Zeeman shift from a spatially varying magnetic field. z B,  ~10 G/cm ~14 MHz/cm Problem: Doppler cooling reduces momentum spread of atoms only.  Similar to a damping or friction force (optical molasses).  Does not reduce spatial spread.  Does not confine the atoms.

10. Magneto-Optical Trap E ee gg 2-level atom 

11. E ee gg magnetic gradient +  z B Magneto-Optical Trap

12.  E ee gg 4-level atom |g   “F=0”, |e   “F=1” 4-level atom |g   “F=0”, |e   “F=1” magnetic gradient + z m F =0 m F =-1 m F =+1 B Magneto-Optical Trap

13.  E ee gg 4-level atom |g   “F=0”, |e   “F=1” 4-level atom |g   “F=0”, |e   “F=1” magnetic gradient + m F =0 m F =-1 m F =+1 z B Magneto-Optical Trap

14.  E ee gg 4-level atom |g   “F=0”, |e   “F=1” 4-level atom |g   “F=0”, |e   “F=1” magnetic gradient + m F =0 m F =-1 m F =+1   z B Magneto-Optical Trap

15.  E ee gg 4-level atom |g   “F=0”, |e   “F=1” 4-level atom |g   “F=0”, |e   “F=1” magnetic gradient + m F =0 m F =-1 m F =+1   z B -- ++ Magneto-Optical Trap

16.  E ee gg 4-level atom |g   “F=0”, |e   “F=1” 4-level atom |g   “F=0”, |e   “F=1” magnetic gradient + m F =0 m F =-1 m F =+1   z B -- ++ Magneto-Optical Trap

17. Magneto-Optical Trap (MOT)

19. ~ 100  K

20. Magneto-Optical Trap (MOT)

21. 10 9 87 Rb atoms

22. Francium MOT PROBLEM: Accelerator produces only 10 6 Fr atoms/s.  Very difficult to work with. SOLUTION: SOLUTION: Attach a Francium Magneto-Optical Trap to the accelerator.  Cold Francium is concentrated in ~1 mm 3 volume.  With T < 100  K, Doppler broadening is negligible.  Long integration times.  Minimally perturbative environment (substrate free).

23. Francium MOT PROBLEM: Accelerator produces only 10 6 Fr atoms/s.  Very difficult to work with. SOLUTION: SOLUTION: Attach a Francium Magneto-Optical Trap to the accelerator.  Cold Francium is concentrated in ~1 mm 3 volume.  With T < 100  K, Doppler broadening is negligible.  Long integration times.  Minimally perturbative environment (substrate free). MOT with ~10 5 210 Fr atoms MOT collection efficiency ~ 1 %