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First Year Seminar: Strontium Project

First Year Seminar: Strontium Project. Outline. Introduction and motivation Second generation cell Polarization spectroscopy and sub-Doppler DAVLL Strontium pyramid MOT 689 nm locking progress. Motivation: Rydberg physics.

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First Year Seminar: Strontium Project

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  1. First Year Seminar: Strontium Project Graham Lochead 03/06/09

  2. Graham Lochead 03/06/09 Outline • Introduction and motivation • Second generation cell • Polarization spectroscopy and sub-Doppler DAVLL • Strontium pyramid MOT • 689 nm locking progress

  3. Motivation: Rydberg physics • We aim to trap ultracold strontium in a 1-D optical lattice and excite to Rydberg states • Rydberg states are states with large n • Rydberg states have large orbital radii Graham Lochead 03/06/09

  4. Graham Lochead 03/06/09 Motivation: Ultracold plasmas • Most plasmas are dominated by their thermal energy • Coulomb coupling parameter  is ratio of Coulomb energy to thermal energy • Strong Coulomb interactions lead to spatial corrrelations • Cold plasma in a spatially ordered lattice will be a first T.C. Killian et al., Physics Reports 449, 77 (2007)

  5. Graham Lochead 03/06/09 Strontium overview • Alkaline-earth element (Group II) • Atomic number 38 84 Sr 0.6% I=0 boson 86 Sr 9.9% I=0 boson 87 Sr 7% I=9/2 fermion 88 Sr 82.5% I=0 boson

  6. Graham Lochead 03/06/09 Electronic structure 3 2 2 1 0 1 3D 3S1 412 nm • 1S0 ground state – no optical pumping • Low decay rate to meta-stable state 3P2 1P1 3P 1D2 461 nm /2p = 32 MHz 689 nm /2p = 7.5 kHz 698nm /2 = 1 mHz 87Sr 1S0 • Broad linewidth for 1S0-1P1 transition • Intercombination line for further cooling

  7. Graham Lochead 03/06/09 Why strontium? • Singly ionised strontium has an optical transition at ~ 422 nm for 2S1/2-2P1/2 • Ion transition can be used for: • imaging • observing charge transfer • laser cooling • Rydberg manipulation T.C. Killian et al., Phys. Rev. Lett., 92:143001, 2004.

  8. Graham Lochead 03/06/09 Laser frequency stabilization “locking” Laser locking requires an atomic sample to investigate the transition And a detection scheme that gives a slope to lock to

  9. Graham Lochead 03/06/09 • Introduction and motivation • Second generation cell • Polarization spectroscopy and sub-Doppler DAVLL • Strontium pyramid MOT • 689 nm locking progress

  10. Graham Lochead 03/06/09 Problems with strontium Locking to a transition requires an atomic sample Atomic strontium has very low vapour pressure Hot strontium reacts with glass and copper M. Asano, K. Kubo J. Nuclear Sci. & Tech. 15 pp. 765~767 (1978)

  11. Graham Lochead 03/06/09 Dispenser technology Sr Sr • Sealed in argon with indium plug • Directional source of atomic vapour • Flux is dependent on current supplied

  12. Graham Lochead 03/06/09 First generation cell Dispenser • Birefringent sapphire windows not required • No continual pumping • No buffer gas • Lifetime estimate ~ 10000 h • Compact size for Sr • Strontium acts as a getter • Only 15-20% absorbtion stable operation A vapor cell based on dispensers for laser spectroscopyE. M. Bridge, J. Millen, C. S. Adams, M. P. A. Jones Rev. Sci. Instr. 80,013101 (2009)

  13. Graham Lochead 03/06/09 Second generation cell 30 cm Dispenser Baffle Designed by Clementine Javaux

  14. Graham Lochead 03/06/09 Second cell absorption • Optically thick for 461 nm transition • Wide Doppler profile due to dispenser type Doppler FWHM of 1.7 GHz at 50% absorption

  15. Second cell saturated absorption Laser 124.5 MHz Probe = 0.14 mW Pump = 7.3 mW Frequency axis calibrated from 86Sr-88Sr splitting Pump Probe Cell 88Sr transition peak is ~5% of the optical depth Graham Lochead 03/06/09

  16. Graham Lochead 03/06/09 • Introduction and motivation • Second generation cell • Polarization spectroscopy and sub-Doppler DAVLL • Strontium pyramid MOT • 689 nm locking progress

  17. Polarization spectroscopy theory J = 1 mJ = -1 0 +1 5s5p 1P1 σ- σ+  Cell 5s2 1S0 J = 0 mJ = 0 M. L. Harris, et al. Phys. Rev. A, 73:062509, 2006. C. P. Pearman et al., J. Phys. B, 35:5141, 2002. Graham Lochead 03/06/09

  18. Polarization spectroscopy setup Laser Frequency calibration Polarization spectroscopy Metal mirror Cell 2 Cell 1 Differential photodiode Graham Lochead 03/06/09

  19. Graham Lochead 03/06/09 Polarization spectroscopy results • Gives a steep gradient – easy to lock to • 0.8 MHz rms offset stability over an hour

  20. DAVLL theory 5s5p 1P1 J = 1 +1 5s5p 1P1 J = 1 0 mJ = -1 0 +1 mJ = -1  σ+  σ- σ- σ+ 5s2 1S0 J = 0 mJ = 0 5s2 1S0 J = 0 mJ = 0 Dichroic Atmoic Vapour Laser Lock (DAVLL) Apply a uniform magnetic field to atomic sample with Helmholtz coils Creates a difference in frequency between different transitions Taking the difference of these signals leads to a dispersion signal with zero crossing at the B=0 transition Graham Lochead 03/06/09

  21. Sub-Doppler DAVLL setup Laser Sub-Doppler DAVLL DAVLL To frequency calibration Metal mirror Coils Differential photodiode M.L. Harris et al., J. Phys. B. Phys.41 085401 Graham Lochead 03/06/09

  22. Graham Lochead 03/06/09 Sub-Doppler DAVLL trace • 3 MHz rms offset stability over an hour

  23. Graham Lochead 03/06/09 Sub-Doppler DAVLL characteristics

  24. Graham Lochead 03/06/09 Laser locking summary • Polarization spectroscopy is used to lock the 461 nm laser with first cell as offset more stable • These two locking schemes have been characterized and written up • Second cell will be used for thermal Rydberg spectroscopy with pulsed dye laser arXiv:0902.1430v1 [physics.atom-ph]

  25. Graham Lochead 03/06/09 • Introduction and motivation • Second generation cell • Polarization spectroscopy and sub-Doppler DAVLL • Strontium pyramid MOT • 689 nm locking progress

  26. Graham Lochead 03/06/09 What is a pyramid MOT? Normal (6 beam) MOT Pyramid MOT K. I. Lee et al., Optics Letters, Vol. 21, Issue 15, pp. 1177-1179

  27. Graham Lochead 03/06/09 Pyramid MOT function Acts as a cold atom source

  28. Graham Lochead 03/06/09 Benefits of a pyramid MOT • Size – much smaller than a Zeeman slower • Blackbody radiation effects reduced

  29. Graham Lochead 03/06/09 Chamber design Trapping gradient of 30 G/cm No water cooling Standard vacuum parts 45 cm Design considerations 30 cm

  30. Graham Lochead 03/06/09 Mirror mount design Most pyramid MOTs are loaded from background atomic vapour or dispensers above pyramid Low vapour pressure and mirrors get coated Problem Solution • Dispensers below mirrors • Slits where mirrors meet in corners

  31. Graham Lochead 03/06/09 The mount design 45 mm Mirror size needs to be small to avoid pumping into meta-stable states

  32. Graham Lochead 03/06/09 Atomic beam divergence measurement Laser Light sheet AOM Expanding lens Atomic beam Light sheet Collimating lens Cylindrical lenses

  33. Graham Lochead 03/06/09 • Introduction and motivation • Second generation cell • Polarization spectroscopy and sub-Doppler DAVLL • Strontium pyramid MOT • 689 nm locking progress

  34. Graham Lochead 03/06/09 Motivation for 689 nm laser 2 1 0 We will use a 532 nm optical lattice laser to add periodic spatial confinement to our MOT Doppler limited temperature 1P1 3P 1D2 461 nm /2p = 32 MHz 689 nm /2p = 7.5 kHz TD≈ 1 mK TD≈ 0.2 μK 1S0

  35. Graham Lochead 03/06/09 Pound-Drever-Hall FPD Oscilloscope PS Laser

  36. Graham Lochead 03/06/09 Pound-Drever-Hall setup Strontium cell FPD Filter Feedback to cavity piezo Slow feedback to piezo PS Fast feedback to diode Laser

  37. Graham Lochead 03/06/09 Slow lock * 100k Ramp PDH signal 100k 1k 10nF 1k * 100k 2k 100k 100 To piezo AD620 510 1k +15V 100k 100k 1k 1k 1k 1k +15V REF02 Unlocked laser has linewidth of ~ 600 kHz Locked laser has linewidth of ~ 350 kHz

  38. Graham Lochead 03/06/09 Cavity lock to atomic transition AOM Going to use frequency modulation spectroscopy as laser already modulated 20 kHz 10 MHz 80 MHz Probe Pump Lock in amplifier Cell Feedback to cavity piezo

  39. Graham Lochead 03/06/09 Summary and future work • Second cell and locking schemes characterized • Pyramid MOT design • 689 nm locking progress • Build the pyramid MOT • Achieve a red MOT • Load 1-D lattice Future work

  40. Saturated absorption spectroscopy fit Sat. spec. fit is achieved by minimizing sum of six Lorentzians in Matlab 1% scaling accuracy for the frequency Parameters Graham Lochead 03/06/09

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