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Graham Lochead 03/06/09 First Year Seminar: Strontium Project Slide 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 Slide 3 Graham Lochead 03/06/09 Motivation: Rydberg physics Rydberg states are states with large n Rydberg states have large orbital radii We aim to trap ultracold strontium in a 1-D optical lattice and excite to Rydberg states Slide 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) Slide 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 Slide 6 Graham Lochead 03/06/09 Electronic structure 1 S 0 ground state no optical pumping Low decay rate to meta- stable state 3 P 2 1S01S0 1P11P1 1D21D2 461 nm /2 = 32 MHz 3P3P 2 1 0 689 nm /2 = 7.5 kHz 412 nm 698nm /2 = 1 mHz 87 Sr Broad linewidth for 1 S 0 - 1 P 1 transition Intercombination line for further cooling 3S13S1 3D3D 3 2 1 Slide 7 Graham Lochead 03/06/09 Why strontium? Singly ionised strontium has an optical transition at ~ 422 nm for 2 S 1/2 - 2 P 1/2 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. Slide 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 Slide 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 Slide 10 Graham Lochead 03/06/09 Problems with strontium M. Asano, K. Kubo J. Nuclear Sci. & Tech. 15 pp. 765~767 (1978) Atomic strontium has very low vapour pressure Hot strontium reacts with glass and copper Locking to a transition requires an atomic sample Slide 11 Graham Lochead 03/06/09 Dispenser technology Sealed in argon with indium plug Directional source of atomic vapour Flux is dependent on current supplied Sr Slide 12 Graham Lochead 03/06/09 First generation cell 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 Dispenser A vapor cell based on dispensers for laser spectroscopy E. M. Bridge, J. Millen, C. S. Adams, M. P. A. Jones Rev. Sci. Instr. 80,013101 (2009) Slide 13 Graham Lochead 03/06/09 Second generation cell DispenserBaffle Designed by Clementine Javaux 30 cm Slide 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 Slide 15 Graham Lochead 03/06/09 Second cell saturated absorption Frequency axis calibrated from 86 Sr- 88 Sr splitting Laser Cell Pump Probe 124.5 MHz Probe = 0.14 mW Pump = 7.3 mW 88 Sr transition peak is ~5% of the optical depth Slide 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 Slide 17 Graham Lochead 03/06/09 Polarization spectroscopy theory 5s 2 1 S 0 5s5p 1 P 1 J = 0 m J = 0 J = 1 m J = -10+1 ++ -- Cell M. L. Harris, et al. Phys. Rev. A, 73:062509, 2006. C. P. Pearman et al., J. Phys. B, 35:5141, 2002. Slide 18 Graham Lochead 03/06/09 Polarization spectroscopy setup Laser Cell 2 Cell 1 Differential photodiode Polarization spectroscopy Frequency calibration Metal mirror Slide 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 Slide 20 Graham Lochead 03/06/09 5s 2 1 S 0 5s5p 1 P 1 J = 0 m J = 0 J = 1 m J = -10+1 ++ -- DAVLL theory 5s 2 1 S 0 5s5p 1 P 1 J = 0 m J = 0 J = 1 m J = -1 0 +1 ++ -- 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 Dichroic Atmoic Vapour Laser Lock (DAVLL) Slide 21 Graham Lochead 03/06/09 Sub-Doppler DAVLL Sub-Doppler DAVLL setup Laser Differential photodiode To frequency calibration Coils DAVLL M.L. Harris et al., J. Phys. B. Phys. 41 085401 Metal mirror Slide 22 Graham Lochead 03/06/09 Sub-Doppler DAVLL trace 3 MHz rms offset stability over an hour Slide 23 Graham Lochead 03/06/09 Sub-Doppler DAVLL characteristics Slide 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] Slide 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 Slide 26 Graham Lochead 03/06/09 What is a pyramid MOT? K. I. Lee et al., Optics Letters, Vol. 21, Issue 15, pp. 1177-1179 Normal (6 beam) MOTPyramid MOT Slide 27 Graham Lochead 03/06/09 Pyramid MOT function Acts as a cold atom source Slide 28 Graham Lochead 03/06/09 Benefits of a pyramid MOT Size much smaller than a Zeeman slower Blackbody radiation effects reduced Slide 29 Graham Lochead 03/06/09 Chamber design 30 cm 45 cm Design considerations Trapping gradient of 30 G/cm No water cooling Standard vacuum parts Slide 30 Graham Lochead 03/06/09 Mirror mount design Low vapour pressure and mirrors get coated Most pyramid MOTs are loaded from background atomic vapour or dispensers above pyramid Problem Solution Dispensers below mirrors Slits where mirrors meet in corners Slide 31 Graham Lochead 03/06/09 The mount design 45 mm Mirror size needs to be small to avoid pumping into meta-stable states Slide 32 Graham Lochead 03/06/09 Atomic beam divergence measurement Laser AOM Expanding lens Collimating lens Light sheet Atomic beam Light sheet Cylindrical lenses Slide 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 Slide 34 Graham Lochead 03/06/09 Motivation for 689 nm laser 1S01S0 1P11P1 1D21D2 461 nm /2 = 32 MHz 3P3P 2 1 0 689 nm /2 = 7.5 kHz T D 1 mK T D 0.2 K We will use a 532 nm optical lattice laser to add periodic spatial confinement to our MOT Doppler limited temperature Slide 35 Graham Lochead 03/06/09 Pound-Drever-Hall Laser FPD PS Oscilloscope Slide 36 Graham Lochead 03/06/09 Pound-Drever-Hall setup Laser FPD PS Filter Slow feedback to piezo Fast feedback to diode Strontium cell Feedback to cavity piezo Slide 37 Graham Lochead 03/06/09 Slow lock Unlocked laser has linewidth of ~ 600 kHz Locked laser has linewidth of ~ 350 kHz Slide 38 Graham Lochead 03/06/09 Cavity lock to atomic transition Going to use frequency modulation spectroscopy as laser already modulated Cell Pump Probe AOM Feedback to cavity piezo 20 kHz 10 MHz Lock in amplifier 80 MHz Slide 39 Graham Lochead 03/06/09 Summary and future work Build the pyramid MOT Achieve a red MOT Load 1-D lattice Second cell and locking schemes characterized Pyramid MOT design 689 nm locking progress Future work Slide 40 Graham Lochead 03/06/09 Saturated absorption spectroscopy fit Isotope Abundance (%) IF Shift (MHz) Rel. Strength 84 Sr0.560--270.81 86 Sr9.860--124.51 87 Sr7.009/2 7/2-9.74/15 9/2-68.91/3 11/2-51.92/5 88 Sr82.580-01 AAmplitude of trace sScaling factor 00 Centre frequency Width cOffset mGradient of background Sat. spec. fit is achieved by minimizing sum of six Lorentzians in Matlab Parameters 1% scaling accuracy for the frequency