Laser System for Atom Interferometry
Andrew Chew
Content
• Overview of related Theory
• Experimental Setup:– Raman Laser System– Frequency/Phase Stabilization
• Outlook
Atom Interferometry
• Similar to Light Interferometry
• Atoms replace role of the light. • Atom-optical elements replace mirrors and beam splitters
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.
Raman Transitions
• Stimulated Raman Transitions result in the super position of |e› and |g› states
• Two phase-locked Lasers of frequency ω1 and ω2 are used to couple the |g,p› and |i,p+ ħk1› states, and the |e, p + ħ(k1-k2)› and |i› states respectively.
• A large detuning Δ suppresses spontaneous emission from the intermediate |i,p+ ħk1› state.
• The ground states are effectively stable.
Ramsey-Bordé Interferometer
• A sequence of π/2, π and π/2 Raman pulses
• 1st π/2 pulse acts a beam splitter: Places the atomic wave in a superposition of |g,p› and |e, p + ħkeff› states
• π pulse acts a mirror: Flips the |g,p› to the |e, p + ħkeff› states and vice versa
• 2nd π/2 pulse acts a beam splitter: Projecting the atoms onto the initial state.
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, 280:443-447, 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.
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
Raman Lasers
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.
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.
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.
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