Laser System for Atom Interferometry

1. Laser System for Atom Interferometry Andrew Chew

2. Content • Overview of related Theory • Experimental Setup: • Raman Laser System • Frequency/Phase Stabilization • Outlook

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

5. 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.

6. 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.

7. Ramsey-Bordé Interferometer • A sequence of π/2, π and π/2 Raman pulses • 1stπ/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 • 2ndπ/2 pulse acts a beam splitter: Projecting the atoms onto the initial state.

8. 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.

9. 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

10. Raman Lasers

11. 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.

12. 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.

13. 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.

14. 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