Laser Cooling And Trapping

MOT

The Magneto-Optical Trap is the first step in this experiment. We use the combination of a magnetic field gradient provided by the quadrupole coils and six intersecting laser beams to trap and cool our atoms. A good, interactive explanation of laser cooling can be found here.

We typically trap 2 x 109 87 Rb atoms and / or 3 x 107 40K atoms using this method. In the photo on the right, you can see a red cloud of 87 Rb atoms being trapped and cooled by a MOT. The red colour is the laser light (780 nm) being scattered from the atoms as they cool. The blue glow of the whole apparatus is the 405 nm LEDs used to desorb atoms from the walls of the glass cell, so that they might be captured from the vapour by the MOT.

MOT_schematic
MOT2.jpg

Features:

  • 4 cm beam diameters
  • Pyrex vacuum cell (7.5 cm x 7.5 cm x 20 cm)
  • Water-cooled quadrupole coils
  • Formed 5 cm below the surface of the atom chip
  • Intensity stabilized power in MOT beams, 400 to 450 mW total power.
  • Dispenser sources. We have used Alvatec and SAES dispensers for 87Rb, and self-made and Alvatec dispensers for 40K. We typically run the dispensers every couple of days to every week.
  • LIAD (light-induced atomic desorption) improves the number of 87Rb atoms in our MOT by a factor of 100. We use ten 405 nm LED illuminators from Epitex to shine about 300 mW total power at the walls of our Pyrex cell.

Molasses


Optical Pumping

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