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

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 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.

7. 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.

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 for Raman lasers and last for the repumper beam

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. 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

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

12. Lasers

13. Fabry Perot ECDL

14. Littrow ECDL

15. 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

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

18. 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

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

20. Results

21. 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

22. 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.