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Rydberg & plasma physics using ultra-cold strontium James Millen Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08.

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Presentation on theme: "Rydberg & plasma physics using ultra-cold strontium James Millen Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08."— Presentation transcript:

1 Rydberg & plasma physics using ultra-cold strontium James Millen Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

2 Outline Spectroscopy of strontium Rydberg states using electromagnetically induced transparency Mauger, Millen, Jones J. Phys. B: At. Mol. Opt. Phys. 40 (2007) F319-F325 Motivation The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

3 Rydberg physics Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 A Rydberg state is one of high principle quantum number n Rydberg atoms can be very large (orbital radius scales as n 2 ) Very strong Rydberg-Rydberg interactions (van-der-Waals interaction scales as n 11 ) This can lead to “frozen” Rydberg gases, where the interaction energy is much greater than the thermal energy. Johannes Rydberg

4 Ultra-cold plasma physics Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Most plasmas are hot, dense and dominated by their kinetic energy The behaviour of ultra-cold neutral plasmas is governed by Coulomb interactions Other “strongly coupled” plasmas are not accessible in the lab Killian, Science

5 Ultra-cold plasma physics Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Plasmas can be formed from cold atoms by optically exciting above the ionisation threshold Some electrons leave, leading to the system being bound The initial electron energy can be set Killian, Science

6 Introduction to Strontium Motivation Atomic Number: 38 An alkaline earth metal (Group II) Four naturally occurring isotopes: 88 Sr (82.6%), 87 Sr (7.0%), 86 Sr (9.9%) & 84 Sr (0.6%) 88,86,84 Sr have no hyperfine structure (Bosonic I=0), 87 Sr has I=9/2 (Fermionic) Negligible vapour pressure at room temperature Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

7 88 Sr energy level diagram Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 1S1S 1P1P 1D1D 3S3S 3P3P 412.7nm 5sns 1 S 0 5snd 1 D nm 32MHz 689nm 7.5kHz 698nm 1mHz ( 87 Sr)

8 Why strontium? Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Singlet-triplet mixing leads to narrow intercombination lines, allowing cooling to <μK This also allows high spectroscopic resolution 1 S 0 ground state can make spectroscopy more simple (no optical pumping required) Singly charged ion Sr + has many transitions in the visible, allowing spatially resolved diagnostics (5s 1 S 0 → 5p 1 P 1 transition is at 420nm)

9 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Spectroscopy of strontium Rydberg states using electromagnetically induced transparency Mauger, Millen, Jones: J. Phys. B: At. Mol. Opt. Phys. 40 (2007) F319-F325

10 The experiment Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/ nm nm 460.7nm Probe Coupling 5s 2 1 S 0 5s5p 1 P 1 5s19s 1 S 0 5s18d 1 D 2 461nm frequency doubled diode laser with tapered amplifier (max. output ~350mW) 420nm frequency doubled diode laser (max. output ~15mW)

11 The experiment Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Probe Coupling Atomic beam 1 2 Oven + Nozzle Strontium is heated in an oven and collimated with a nozzle The transmission of the probe beam is measured as it is scanned across the transition When the coupling beam is turned on there is an increase in the transmission of the probe beam on resonance Mohapatra, Jackson, Adams Phys. Rev. Lett

12 Electromagnetically induced transparency Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 When the probe laser is scanned across the transition at 460.7nm you see a Doppler broadened absorption profile By subtracting the Doppler broadened background this peak can be studied. It can have a width as small as 5MHz. When the coupling laser is resonant with the transition under investigation there is an increase in transmission on the probe beam ~150MHz ~5MHz

13 Frequency axis calibration Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/ MHz Saturated absorption spectroscopy was used to resolve the 5s 1 S 0 → 5p 1 P 1 lines for 88 Sr and 86 Sr IsotopeAbundance % IFShift (MHz) Rel. Strength 84 Sr Sr /2 7/2-9.74/15 87 Sr 9/ /3 11/ /5 88 Sr Eliel et. al. Z. Phys. A 311 1, Kluge & Sauter Z. Phys MHz A fit based on the sum of six Lorentzians was used. Scaling parameter was used to calibrate the frequency axis

14 Fitting – EIT peaks Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 In order to fit to our EIT lineshapes we use the following expression for the susceptibility χ(v) † γ 3 is the decay rate of the Rydberg state, and includes all line broadening mechanisms as well as the natural lifetime We sum over all four isotopes, and integrate the absorption over the transverse velocity distribution The absorption is given by the imaginary part of the susceptibility † Xiao, Li, Jin, Gea-Banacloche Phys. Rev. Lett

15 Isotope shift of EIT peaks Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Coupling laser tuned to the 5s5p 1 P 1 → 5s18d 1 D 2 transition Signal / V Time / s 88 Sr 86 Sr 1) 2) 3) 4)

16 Isotope shift of EIT peaks - Results Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Coupling tuned near 5s18d 1 D 2 transition Coupling tuned near 5s19s 1 S 0 transition Singlet-triplet mixing with the 5s18d 3 D 3 state cause massive (~GHz) hyperfine splitting in 87 Sr, so the peak isn’t visible † † Beigang et. al. J. Phys. B: At. Mol. Phys. 15 L201-L206 The transition to the 5s19s 1 S 0 is much weaker than to the D state, so a lock-in amplifier was used

17 Doppler mismatch Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Due to the difference in wavevectors between the probe and coupling beams you cannot read the shift straight from the frequency axis Δω p = -{ (1 - λ c /λ p )Δω 2 + (λ c /λ p )Δω 3 } (~0.1)(~0.9) Transition 88 Sr → 86 Sr (MHz) 88 Sr → 87 Sr (MHz) 5s 2 1 S 0 → 5s18d 1 D 2 226±7- 5s 2 1 S 0 → 5s19s 1 S 0 213±762±8

18 Further study Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Oven + Nozzle Probe Coupling Atomic beam 1 2

19 Further study Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Oven + Nozzle Probe Coupling Atomic beam 1 2

20 Strontium energy level diagram Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 1S1S 1P1P 1D1D 3S3S 3P3P 5sns 1 S 0 5snd 1 D nm 32MHz 420nm 689nm 7.5kHz 698nm 1mHz ( 87 Sr)

21 Beam translation Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Oven + Nozzle Probe Coupling Atomic beam 1 2 Translatable mirror The original beam separation was set by the beamsplitter to 4mm A translatable mirror enabled separations of 3- 13mm Varied probe power from μW Results were inconclusive Could be Rydberg autoionization

22 Rydberg Autoionization Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 5s 2 1 S 0 5s5p 1 P 1 5sns 1 S 0 5pns 1 P 1 5s 1 S 0 460nm420nm e-e- SrSr + e-e- e-e- e-e- e-e- Sr 2+

23 Conclusion Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Electromagnetically induced transparency provides a useful, non-destructive spectroscopic tool The population dynamics of our system are not well understood, further modelling is required EIT could be used for laser stabilization Need to move towards cold strontium to fulfil our aims of studying “frozen” Rydberg gases and plasmas

24 The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

25 Requirements The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Three orthogonal axis for a blue (460.7nm) MOT Potential for a red (689nm) MOT (sub μK cooling) Axis for a dipole trap MOT from Tino group: LENS, Florence Detection via a micro channel plate (MCP) Electrodes for charged particle control / state- selective field ionisation MOT coils inside chamber Axis for excitation of atoms and imaging

26 The vacuum system The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

27 The chamber 30cm flange to flange 12 DN40 flanges (separated by 30°) 2 DN200 flanges, one with 8’’ viewport, the other with 1.5’’ viewport and feed- throughs Beam height is 190mm above optical bench The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

28 Internals – MOT coils The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Coils wound from 1mm Kapton insulated copper wire Can produce a field gradient of 30Gcm -1 at 2.5A Mounted directly on top flange so can directly “plug” into the chamber No electrical connections in any optical path

29 The electrodes The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Split ring geometry mounted onto MOT coil formers Blocks no optical access 8 independently controllable electrodes Can produce reasonably flat fields and also gradients

30 Calculating the electric field The electric potential (in 2D) Φ(x,y) is the solution to Laplace’s equation Φ(x,y) xx + Φ (x,y) yy = 0 Map Φ(x,y) onto an array of points with spacing h Taylor expand [Φ(x±h,y) + Φ (x,y±h) + Φ(x ±h,y±h)] = 8Φ(x,y) + 3h 2 (Φ(x,y) xx + Φ(x,y) yy ) + O(h 4 ) 0 → Φ(x,y) ≈ 1/8[ Φ(x±h,y) + Φ (x,y±h) + Φ(x ±h,y±h)] The average of all neighbouring points The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

31 Realization in MatLab The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Create a 40x40x40 array Set an initial electrode configuration Use the “circshift” command to take average of neighbouring points Image across various slices

32 Field calculations The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Field changes by <1% in central 4mm cube

33 Online resources See website: The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

34 The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Current progress - Apparatus Pumped down to ~ Torr New oven currently being built Waiting to move into new lab

35 The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Conclusion We have shown that EIT can be used as a spectroscopic tool for strontium Our apparatus for cooling and trapping strontium is almost complete Once we have achieved a MOT we can move towards creating an ultra-cold Rydberg gas or neutral plasma

36 Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Team Strontium would like to thank you for your attention


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