Laser System for Atom Interferometry

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Laser System for Atom Interferometry

• Andrew Chew

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Content

• Overview of related Theory
• Experimental Setup
• Raman Laser System
• Frequency/Phase Stabilization
• Outlook

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Atom Interferometry

• Similar to Light Interferometry
• Atoms replace role of the light.
• Atom-optical elements replace mirrors and beam
  splitters

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Motivation

• Light Interferometry is used to make inertial
  sensors but the long wavelength limits the
  resolution of the phase measurement.
• The atomic de Broglie wavelength is much shorter
  and thus allows for greater resolution of the
  phase measurement.
• Atoms have mass and thus we can make measurements
  of the forces exerted on them.
• An example would be the measurement of the
  gravitation force.

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Raman Transitions

• Stimulated Raman Transitions result in the super
  position of e and g states
• Two phase-locked Lasers of frequency ?1 and ?2
  are used to couple the g,p and i,p hk1
  states, and the e, p h(k1-k2) and i states
  respectively.
• A large detuning ? suppresses spontaneous
  emission from the intermediate i,p hk1 state.
• The ground states are effectively stable.

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Ramsey-Bordé Interferometer

• A sequence of p/2, p and p/2 Raman pulses
• 1st p/2 pulse acts a beam splitter Places the
  atomic wave in a superposition of g,p and e, p
  hkeff states
• p pulse acts a mirror Flips the g,p to the
  e, p hkeff states and vice versa
• 2nd p/2 pulse acts a beam splitter Projecting
  the atoms onto the initial state.

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Laser System

• Extended Cavity Diode Laser (ECDL) design used by
  Gilowski et. al in Narrow bandwidth interference
  filter-stabilized diode laser systems for the
  manipulation of neutral atoms. Optics
  Communications, 280443-447, 2007.
• 3 Master Oscillator Power Amplifier (MOPA)
  systems for each wavelength, each consisting of
  an ECDL as the seeder and a Tapered Amplifier as
  the amplifier. One MOPA is for cooling, another
  two for Raman lasers.
• Repumper laser consisting of one DFB laser diode.

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Experimental Setup

• Laser system for Rubidium consisting of cooling
  and repumper lasers for preparation of atomic
  cloud.
• Raman laser system for atom interferometry.
• Laser system for imaging and detection of
  internal atomic states.
• 1 set of laser systems for each individual
  species of atoms used for interferometry

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Raman Lasers
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Raman Lasers

• The Raman lasers must be stabilized to stable
  frequency references to ensure that the frequency
  separation between them is kept at 6.84GHz.
• The Raman lasers are overlapped to produce the
  laser beat note.
• The laser beat note is amplified and mixed with a
  7GHz reference oscillator then filtered with a
  low-pass filter to produce a 160MHz signal.

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Raman Lasers

• The beat note is then passed into a PLL board
  where the frequency divided by 2 and then is
  compared against a 80MHz frequency reference
  using a digital phase-frequency detector.
• The signal is then filtered, integrated and two
  outputs are produced one fast and one slow for
  the laser current and the laser piezo feedback.

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Vacuum System

• Vacuum Chamber consists of 2 glass cells and a
  central metallic vacuum chamber.
• A Titanium Ion-Getter Pump and A Titanium
  Sublimation pump is attached to the Vacuum
  chamber
• The Ion Getter pump operates continuously, while
  the Titanium Sublimation pump is operated
  initially during baking and then switched off.
• There are dispensers to introduce the Rubidium
  and Cesium atoms into the vacuum system.
• Prior to use, the vacuum system is baked with a
  rotary vane pump and a turbomolecular pump
  running together with other two pumps.
• A Mass Spectrometer is used to monitor the gas
  pressure levels.
• We need a vacuum pressure of 10-10 mbar.

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Outlook

• Near term we plan to complete the PLL for the
  Raman Lasers
• Next step is the Characterize the PLL
• And then work on other aspects such as getting
  the detection beam ready etc.
• Then We can do interferometry of Rubidium