A MagnetoOptical Trap

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A Magneto-Optical Trap for Strontium
James Millen
A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
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Outline

• Optics
• Trapping strontium
• Laser system
• Physical layout

• Electronics
• Imaging the MOT
• Disaster strikes!
• Solution

A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
3
Trapping strontium

• Strontium has no appreciable vapour pressure at
  room temperature
• ? An oven is required

• This hot beam of strontium needs to be slowed
  down to be trapped
• ? A Zeeman slower is required

• The strontium is trapped in a Magneto-Optical
  Trap (MOT), which requires 3 pairs of
  counterpropagating beams (shown) and coils to
  produce a magnetic field (internal)

A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
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Laser System
(All frequencies quoted relative to the 5s2 1S0
? 5s5p 1P1 transition in 88Sr)
Spectroscopy Locking our laser using POLWIS
Double pass at 120MHz ? 0 MHz
Imaging For absorption imaging
Double pass at 120MHz ? 0 MHz
-240MHz
Double pass at -136MHz ? 512 MHz
Zeeman Slower
Toptica frequency doubled laser system at 461nm
Single pass at 200MHz ? -40 MHz
MOT beams
A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
5
Physical layout
A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
6
Physical layout
A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
7
Imaging the MOT

• Using a Photodiode we can gather temporal
  information about the MOT
• We need to be able to turn the MOT on and off
  remotely
• One has to be careful with the inductance of the
  coils
• Need a switching circuit that can also dump power
  when the coils are off

A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
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Switching circuit
Feedback
Follower
Integrator
Switch
A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
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Disaster!

• There are two MOT coils in our chamber, which can
  be electrically isolated
• One coil is shorted to the chamber (ground)

• The power supply is floating, so who cares?
• The switch is grounded via the TTL supply.
  Current leaks about 1/3rd of the way along the
  coil

A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
10
Solution
Isolate the ground of the TTL using an
optocoupler, and allow the switch to float.
A Magneto-Optical Trap for Strontium Group
meeting 29/09/08
11
Stop press!
MOT fluorescence
Coil switch on/off
A Magneto-Optical Trap for Strontium Group
meeting 29/09/08