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(Towards) Extreme Ultraviolet Frequency Comb Spectroscopy of Helium and Helium+ Ions

Kjeld Eikema. (Towards) Extreme Ultraviolet Frequency Comb Spectroscopy of Helium and Helium+ Ions. Jonas Morgenweg , Itan Barmes , Tjeerd Pinkert Dominik Kandula , Chirstoph Gohle , Anne Lisa Wolf, Stefan Witte. VU University, Netherlands. € from.

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(Towards) Extreme Ultraviolet Frequency Comb Spectroscopy of Helium and Helium+ Ions

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  1. Kjeld Eikema (Towards) Extreme Ultraviolet Frequency Comb Spectroscopy of Helium and Helium+ Ions Jonas Morgenweg, ItanBarmes, TjeerdPinkert DominikKandula, ChirstophGohle, Anne Lisa Wolf, Stefan Witte VU University, Netherlands € from ECT* 28 September – 2 november 2012 "Proton size conundrum"

  2. Outline • Introduction • To the XUV (at 51-85 nm) with frequency combs: • Two-pulse “Ramsey Comb” excitation. • The next generation: “Ramsey-Fourier-Frequency Comb” • First signal with two-pulse two-photon excitation in Rb • Summary en Outlook

  3. Frequency comb laser activities @ LaserLaB XUV comb metrology, QED tests: Jonas Morgenweg, Tjeerd Pinkert, Itan Barmes, Dominik Kandula, Christoph Gohle Precision spectroscopy on ions: Anne Lisa Wolf, Jonas Morgenweg, Wim Ubachs, Steven v.d. Berg 51 nm = 6 PHz 15w Coherent control: Itan Barmes, Stefan Witte Dual-comb spectroscopy & mid-IR combs: Axel Ruehl, AlissioGambetta, Marco Marangoni et al. Precision frequency comb calibrations, collaborations with: Wim Ubachs, Jeroen Koelemeij, Rick Bethlem, and others. Wim Vassen: He 2 3S1 - 2 1S0 transition, Science 333, 196-198 (2011) 100µm Precision dissemination over fiber: Tjeerd Pinkert, Jeroen Koelemeij

  4. Hydrogen 2S 243 nm 243 nm 1S Introduction QED / Ry issues? Muonic-hydrogen 6 mm 2P 2S 2 keV… 1S R. Pohl et al, Nature, vol. 466, pp. 213-216 (2010). C.G. Parthey et al., PRL 107, 203001 (2011) 1S-2S: 2 466 061 413 187 035 (10) Hz

  5. Comparison normal vs. muonic matter H He+ mH mHe+ Energy Energy 2P 812 nm 2P 6 mm 2S 2S 2S 2x 60 nm 0.15 nm (8.2 keV) 0.6 nm (2 keV) 2S 2x 243 nm 1S 1S 1S 1S

  6. The 1S-2S values for H and mH Scaling He+ (kHz) H (kHz) Theory Du1S-2S 2.466...×1012 9.869...×1012 Z2 G1S-2S 1.3×10-3 83×10-3 Z4 DL1S-2S 7 127 887(44) 93 856 127(348)* Z≥3.7 Finite size 1102(44) 62 079(295) Z4r2 (nucl. pol.) (2) (40 or 15**) -8(3) -543(185) Z≥6 B60+B7i 7% or 4%*** 25% Test B60+B7i Rel. acc. DL1S-2S 6.3 ppm 3.7 ppm**** Experiment Du1S-2S 246606143187.035(10) not measured 16 65 dL(dR∞)1S-2S Z2 2.2 ppm 0.7 ppm Rel. dL(dR∞) H 1S-2S from C.G. Parthey et al., PRL 107, 203001 (2011)

  7. The experimental challenge Hydrogen Helium Helium+ 2S <30 nm 2x 60 nm 1s5p 1s2s 2x 120 nm 2S 51 nm 2x 243 nm 1S 1s2 1S

  8. Frequency comb lasers Mode-locked laser T Frequency Comb laser w Nobel Prize Physics 2005 T.W. Hänsch R.J. Glauber J. Hall

  9. φCE= 0 φCE= p/2 time vg≠ vφ Frequency comb lasers T f0 = frep x φCE / 2 frep = 1/T Int. fn= f0 + n.frep frequency 0 R. Holzwarth et al. PRL 85, 2264 (2000), D.J. Jones et al. Science 288, 635 (2000)

  10. Frequency comb lasers as optical rulers T Frequency Comb laser w Single-mode laser freq. f beat note measurement; f = f0 + n frep + fbeat Experiment

  11. Direct frequency comb excitation T Frequency Comb laser Experiment w Single-mode laser freq. f beat note measurement; f = f0 + n frep +fbeat Experiment

  12. Upconversion through high-harmonic generation Noble gas jet XUV (l<100 nm) IR pulses 1014 W/cm2 NIR (800 nm) UV VUV XUV X-RAY DUV 3rd 5th 7th 9th 333rd harmonic conversion … frequency

  13. High-harmonic generation (HHG) IR ~1014 W/cm2 Corkum & Krausz, Nature Physics 3, 381 (2007)

  14. Phase coherence of HHG Phase XUV ~ -a IIR R. Zerne et al., PRL 79, 1006 (1997) Other experiments: E.g. excitation Kr continuum @ 88 nm, delays~ 100 fs – ps range Cavalieri et al., PRL 13, 133002 (2002) A. Pirri et al. PRA 78, 043410 (2008) and more

  15. Frequency comb up-conversion XUV pth harmonic: Near-Infrared: fn = p f0 + m frep fn = f0 + n frep IR UV harmonic conversion VUV XUV DUV X-RAY frequency

  16. XUV comb generation methods HHG in resonator (MPQ, JILA, Arizona, etc.) C. Gohle et al. Nature 436, 234 2005 A. Ozawa et al., PRL 100, 253901 (2008) R.J. Jones et al. PRL 94, 193201 (2005) I.Hartl et al. Opt. Lett. 32, 2870 (2007), Etc. A. Cingoz et al., Nature 842, 68 (2012) Argon spectroscopy at 82 nm, 3 MHz acc. HHG after amplification (LaserLaB Amsterdam) S. Witte et al. Science 30, 400 (2005) Zinkstok et al. PRA 73, 061801(R) (2006) T.J. Pinkert et al. OL 36, 2026 (2011) (argon 85 nm, neon 60 nm, helium 51 nm) D. Kandula et al. PRA 84, 062512 (2011) D. Kandula et al. PRL 105, 063001 (2010) Helium spectroscopy at 51 nm, 6 MHz acc.

  17. φCE= 0 φCE= p/2 time vg≠ vφ Frequency comb lasers – infinite pulse train T f0 = frep x φCE / 2 frep = 1/T Int. fn= f0 + n.frep frequency 0

  18. Frequency comb lasers - two pulses T φCE= 0 φCE= p/2 time vg≠ vφ f0 = frep x φCE / 2 frep = 1/T Int. fn= f0 + n.frep frequency 0

  19. c(2) fluorescence cone signal pump wp, kp   seed idler ws, ks  i p s i = p – s Parametric chirped pulse amplification BBO crystals pumped by 532 nm at intensities of 7 GW/cm2 • Tuning over 700-1000 nm with little effort • Bandwidth adjustable from 300 nm to 5 nm • No memory effect • Two comb pulses amplified by two synchronized equal pump pulses; microradian pointing sensitivity!

  20. HHG of two pulses IXUV ~ IIR9 f=50 cm <1014 W/cm2 XUV pulses few nJ levelDivergence <2 mrad IR pulses – mJ level

  21. At the 15th harmonic to excite He 6.6 ns (51 nm) Helium HHG 15w 1S5P 6 MHz DfCE ~ l/300 1S2S 51.6 nm 1S2 15w

  22. Principle and setup schematic overview

  23. Ramsey comb excitation of helium at 51 nm 121 MHz Contrast up to 60% at higher rep-rate: 50 as jitter D. Kandula et al. PRL 105, 063001 (2010) D. Kandula et al. PRA 84, 062512 (2011)

  24. He ground state measurement systematics • IR phase shifts in OPA • Pulse phase front tilt • Spectral/temporal phase difference between pulses • Doppler shift: varying speed using He, He/Ne, He/Ar & tune angle • Ionization: varying density, pulse intensity ratio • Adiabatic shift in HHG • shift in HHG due to excitation • AC Stark shifts (IR, XUV, ioniz. l.), • DC Stark (field free) • Self-phase modulation (pulse ratio). • Recoil shift 18.5 MHz for 5p • Many more efects!:Tests of chirp, HHG focus position, f0, out-of-centre phase, ....etc.

  25. Theory and experiment Accuracy 6 MHz (8 fold improvement) Drake Pachucki S. Bergeson et al. Eikema et al. blue = experiments and red = theory

  26. History of the He ground state energy accuracy Blue = experiment Red = theory

  27. Tunable XUV Ramsey frequency comb Helium Argon Neon ~60 nm (13th harm. in Kr) ~84 nm (9th harm. in Xe) ~51 nm (15th harm. in Kr) T.J. Pinkert et al. OL 36, 2026 (2011)

  28. View of the lab

  29. HHG and excitation apparatus

  30. Apparent two-pulse limitation: T and fs Signal = cos(wtr T – fs) An error in fs gives a frequency error in wtr of Dwtr = fs / T fs T

  31. The magic of Fourier transformation Signal = cos(wtr T – fs) FFT fs wtr T

  32. The magic of Fourier transformation Signal = cos(wtr T – fs) FFT fs wtr T FFT wrep fs fs wtr wrep = 2p/T 2T T

  33. FC-FTS vs. FC Full-rep-rate excitation Full rep. rate coherent addition wrep fs fs fs 2T T wtr wrep = 2p/T Two-pulse incoherent addition FFT wrep fs fs wtr wrep = 2p/T 2T T

  34. AC-Stark shift Full rep. rate coherent addition wrep fStark 2fStark 3fStark 2T T wtr wrep = 2p/T Two-pulse incoherent addition FFT wrep fStark fStark wtr wrep = 2p/T 2T T

  35. FC-FTS features and requirements • Accuracy and resolution equivalent to full-rep rate excitation • FC-FFT more easily tunable at extreme wavelengths • AC-Stark shift 'free', in contrast to full-rep rate excitation • With more than 1 transition: ’interference’ effects, but possibleto model. Simulations for T=160 ns show ~10 kHz accuracy • Requirements: • IR FC pulses must be amplified with constant phase and energy, ideally < l/1000 and <1% energy fluctuation,irrespective of the time delay between the pulses!

  36. The old situation with a delay line Relay imaging 7 ps osc. 1064 nm regen amp. 2 mJ power amp. 2 x 200 mJ SHG sync. comb laser ~780 nmfrep=150 MHz 3-stage NOPCPA 2x 2 mJ 200 fs @ 30 Hz D. Kandula et al., Opt. Express, 16, 7071-7082 (2008)

  37. The old situation with a delay line SHG sync. comb laser ~780 nmfrep=125 MHz 3-stage NOPCPA

  38. The new system pulse picking & scaling 10 psosc. 1064 nm 'bounce' amp 2 x 1 mJ power amp. 2 x 120 mJ EOM/AOM SHG sync. T comb laser ~780 nmfrep=125 MHz 3-stage NOPCPA 2x 2 mJ 10-200 fs, T=8 ns to >10 ms rep. rate 300 Hz J. Morgenweg and K.S.E. Eikema, OL 37, 208 (2012) J. Morgenweg and K.S.E. Eikema, Las. Phys. Lett. 5, 1 (2012)

  39. New pump laser front-end 2x 1 mJ Dt = 8 ns to >10 ms Rep. rate < 1 kHz 2x 100 mJ 30 Hz rep. rate (300 Hz in prep.)

  40. (Bounce) amplifier performance (n=7; Tosc ~ 8 ns) (n=35) (n=160)

  41. Amplified comb pulses - phase measurement Single shot differential spectral interferometry Single shot SNR sufficient for 10-20 mradrms stability Inaccuracy < 5mrad Oscillator MZ-Interferometer Analysis BS10% CCD Camera OPCPA HHG Spectr. BS 50 % NG PC SP-Filter Fiber BS 5% PC Pulse separation

  42. Phase of the amplified comb pulses Average phase equal within 5 mrad (l/1200)and pulse energy equal within 1% for a 2-pulse delay (16 ns) to 32-pulse delay (256 ns) Delay Laser shots

  43. Doppler-’free’ comb excitation in Rb CW lasers: Hansch et al., OC 11, 1 (1974) Nanosecond pulses: Biraben et al., PRL 32, 12 (1974) Picosecond pulses: Fendel et al., OL 32, 6 (2007) Femtosecond pulses, and with spatial coherent control: I. Barmes et al., to be published in Nature Photonics

  44. Elimination of background by coherent control Transform-limited 100µm V-shaped phase 100µm

  45. Two-photon two-pulse Fourier-Ramsey-Comb Excitation of Rb (5S – 7S) n=2; T=15.9 ns n=4; T=31.8 ns Fluorescence signal n=2; T=63.5 ns Inter-pulse delay T in femtoseconds

  46. Summary and Outlook • XUV frequency comb metrology demonstrated, 85-50 nm Ground state energy of helium with an accuracy of 6 MHz • Fourier-Ramsey Frequency Comb Excitation with 2 pulsesNew system and first spectroscopy in Rb shown • Few mrad variation over 256 ns; potentially <kHz XUV accuracy • Outlook: He+ in an ion trap with Be+ cooling for 1S-2S spectr., • Two-photon (2*120 nm) in Helium with coherent control, Two-photon in H2 to improve ionization potential to <100 kHz • Delay extension up to 100’s of ms for Hz-level accuracy? Ions in a Paul trap T.J. Pinkert et al. Opt. Lett. 36, 2026 (2011) J. Morgenweg et al. Opt. Lett. 37, 208 (2011) D. Kandula et al. PRL 105, 063001 (2010) D. Kandula et al. PRA 84, 062512 (2011) I. Barmes et al., Nature Photonics, to be published

  47. The people Axel Ruehl Tjeerd Pinkert JonasMorgenweg Stefan Witte Itan Barmes Wim Ubachs RoelZinkstok Christoph Gohle Dominik Kandula AmandineRenault Anne LisaWolf

  48. From here on additional slides

  49. Coherent control for Doppler-reduced excitation

  50. Full spatial coherent control

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