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

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

Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Rydberg physics A Rydberg state is one of high principle quantum number n Rydberg atoms can be very large (orbital radius scales as n2) Very strong Rydberg-Rydberg interactions (van-der-Waals interaction scales as n11) This can lead to “frozen” Rydberg gases, where the interaction energy is much greater than the thermal energy. Johannes Rydberg 1854-1919 Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Ultra-cold plasma physics 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 316 705-708 Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Ultra-cold plasma physics 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 316 705-708 Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

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

Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 88Sr energy level diagram 5sns 1S0 5snd 1D2 412.7nm 460.7nm 32MHz 689nm 7.5kHz 698nm 1mHz (87Sr) 1S 1P 1D 3S 3P Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Why strontium? Singlet-triplet mixing leads to narrow intercombination lines, allowing cooling to <μK This also allows high spectroscopic resolution 1S0 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 1S0 → 5p 1P1 transition is at 420nm) Motivation 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 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

420nm frequency doubled diode laser (max. output ~15mW) The experiment 420.47nm 420.40nm 460.7nm Probe Coupling 5s2 1S0 5s5p 1P1 5s19s 1S0 5s18d 1D2 461nm frequency doubled diode laser with tapered amplifier (max. output ~350mW) 420nm frequency doubled diode laser (max. output ~15mW) Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Strontium is heated in an oven and collimated with a nozzle The experiment 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. 98 113003 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

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

Frequency axis calibration A fit based on the sum of six Lorentzians was used. Scaling parameter was used to calibrate the frequency axis Saturated absorption spectroscopy was used to resolve the 5s1S0→ 5p1P1 lines for 88Sr and 86Sr 124.5 MHz Isotope Abundance % I F Shift (MHz) Rel. Strength 84Sr 0.56 - -270.8 1 86Sr 9.86 -124.5 7.00 9/2 7/2 -9.7 4/15 87Sr -68.9 1/3 11/2 -51.9 2/5 88Sr 82.58 32 MHz Eliel et. al. Z. Phys. A 311 1, Kluge & Sauter Z. Phys. 270 295 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Fitting – EIT peaks In order to fit to our EIT lineshapes we use the following expression for the susceptibility χ(v)† γ3 is the decay rate of the Rydberg state, and includes all line broadening mechanisms as well as the natural lifetime The absorption is given by the imaginary part of the susceptibility We sum over all four isotopes, and integrate the absorption over the transverse velocity distribution †Xiao, Li, Jin, Gea-Banacloche Phys. Rev. Lett. 74 666 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Isotope shift of EIT peaks Coupling laser tuned to the 5s5p1P1→5s18d1D2 transition 1) 2) Signal / V 88Sr Signal / V 88Sr Time / s Time / s 86Sr 3) 4) 86Sr 88Sr Signal / V Signal / V 88Sr Time / s Time / s Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Isotope shift of EIT peaks - Results Coupling tuned near 5s18d1D2 transition Singlet-triplet mixing with the 5s18d3D3 state cause massive (~GHz) hyperfine splitting in 87Sr, so the peak isn’t visible† Coupling tuned near 5s19s1S0 transition The transition to the 5s19s1S0 is much weaker than to the D state, so a lock-in amplifier was used †Beigang et. al. J. Phys. B: At. Mol. Phys. 15 L201-L206 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Doppler mismatch Due to the difference in wavevectors between the probe and coupling beams you cannot read the shift straight from the frequency axis Δωp = -{ (1 - λc/λp )Δω2 + (λc/λp)Δω3 } (~0.1) (~0.9) Transition 88Sr→86Sr (MHz) 88Sr→87Sr 5s2 1S0→5s18d1D2 226±7 - 5s2 1S0→5s19s1S0 213±7 62±8 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

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

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

Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08 Strontium energy level diagram 5sns 1S0 5snd 1D2 420nm 460.7nm 32MHz 689nm 7.5kHz 698nm 1mHz (87Sr) 1S 1P 1D 3S 3P Motivation Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

The original beam separation was set by the beamsplitter to 4mm Beam translation The original beam separation was set by the beamsplitter to 4mm A translatable mirror enabled separations of 3-13mm Varied probe power from 30-180μW Results were inconclusive Could be Rydberg autoionization Coupling 1 2 Atomic beam Oven + Nozzle Translatable mirror Probe Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Rydberg Autoionization 5s2 1S0 5s5p 1P1 5sns 1S0 5pns 1P1 5s 1S0 e- e- e- e- Sr+ Sr2+ Sr Sr+ e- 460nm 420nm 420nm Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

EIT could be used for laser stabilization Conclusion 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 Spectroscopy of strontium Rydberg states using EIT Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

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 Requirements 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 Axis for excitation of atoms and imaging Detection via a micro channel plate (MCP) Electrodes for charged particle control / state-selective field ionisation MOT coils inside chamber The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

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

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

Coils wound from 1mm Kapton insulated copper wire Internals – MOT coils 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 The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

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

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) + 3h2(Φ(x,y)xx + Φ(x,y)yy) + O(h4) → 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

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

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

See website: http://massey.dur.ac.uk/resources/lab_resources.html Online resources See website: http://massey.dur.ac.uk/resources/lab_resources.html The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Current progress - Apparatus Pumped down to ~ 10-10 Torr New oven currently being built Waiting to move into new lab The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

Our apparatus for cooling and trapping strontium is almost complete 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 The ultra-cold strontium experiment Rydberg & plasma physics using ultra-cold strontium– Seminar 28/05/08

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