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 ω 1 and ω 2 are used to couple the |g,p› and |i,p+ ħk 1 › states, and the |e, p + ħ(k 1 -k 2 )› and |i› states respectively. A large detuning Δ suppresses spontaneous emission from the intermediate |i,p+ ħk 1 › state. The ground states are effectively stable.

Ramsey-Bordé Interferometer A sequence of π/2, π and π/2 Raman pulses 1 st π/2 pulse acts a beam splitter: Places the atomic wave in a superposition of |g,p› and |e, p + ħk eff › states π pulse acts a mirror: Flips the |g,p› to the |e, p + ħk eff › states and vice versa 2 nd 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: , 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

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 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