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Towards a Laser System for Atom Interferometry

Towards a Laser System for Atom Interferometry. Andrew Chew. Content. Overview of related Theory Experimental Setup: Laser System Frequency Stabilization Characterisation of realized Lasers Outlook. Atom Interferometry. Similar to Light Interferometry Atoms replace role of the light.

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Towards a Laser System for Atom Interferometry

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  1. Towards a Laser System for Atom Interferometry Andrew Chew

  2. Content • Overview of related Theory • Experimental Setup: • Laser System • Frequency Stabilization • Characterisation of realized Lasers • Outlook

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

  4. 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.

  5. 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.

  6. 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.

  7. 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 for Raman lasers and last for the repumper beam

  8. 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

  9. ECDL Design • Cavity Length Defined by the distance between the laser diode and the cavity mirror/output coupler. • Output coupler mounted on a piezo-electric transducer which is partially transmitting and reflecting. • Inside the cavity, the emitted laser beam is collimated using a collimating lens, and then focused onto the output coupler, forming a very stable angular insensitive cavity. • DFB laser diode which promises narrow linewidth is used

  10. Laser Operation • Tuning of wavelength by changing • Laser diode current (Fast MHz time scale) • Cavity length (acoustic time scale, kHz) • Temperature (Hz time scale)

  11. Lasers

  12. Fabry Perot ECDL

  13. Littrow ECDL

  14. Laser Characterization • Heterodyne 2 lasers to obtain their beat note in a optical setup shown below • Linewidth of the beat note corresponds to: • We need 3 lasers and beat each one with each other to obtain a system of 3 simultaneous equations

  15. Laser Characterization • We will beat 3 lasers: 1 ECDL laser using a DFB ECDL, an Edge Emitting ECDL and a Littrow ECDL laser

  16. Beat Note • DFB ECDL and Edge Emitting ECDL Beat Linewidth: 0.4775 +/- 0.0300 MHz • Sweep Rate: 30ms • Bandwidth: 30KHz • DFB ECDL and Littrow ECDL Beat Linewidth: 0.4910 +/- 0.0276 MHz • Sweep Rate: 30ms • Bandwidth: 30KHz

  17. Beat Note • Edge Emitting Diode and Littrow ECDL Beat Linewidth: 0.5295 +/- 0.0356 MHz • Sweep Rate: 30ms • Bandwidth: 30KHz

  18. Results

  19. Analysis • The Spectrum Analyzer was set to have a fast sweep rate setting of 30ms as the free running DFB and Fabry Perot ECDL have a slow frequency drift of a few MHz within 100ms timescale. • A more ideal setup would require all 3 lasers locked to an atomic reference during the measurement. • The DFB ECDL, as expected, has the narrowest linewidth of all the 3 lasers

  20. Outlook • The Laser system is characterized and we will now proceed to build the tapered amplifier to form the MOPA system. 2 other MOPAs will also be constructed • Vacuum system for experiment will be constructed. • We want to do inertial measurements by year-end. • Laser system for the second atomic species will also need to be set up and characterized.

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