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High precision spectroscopy of atomic hydrogen

High precision spectroscopy of atomic hydrogen. J. Alnis, A. Matveev, N. Kolachevsky, Th. Udem, T. Hänsch. Energy levels Of H atoms. „ Hänsch curve“ Precision optical spectroscopy of H atoms. H against Cs frequency measurements with 14 digits of precision

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High precision spectroscopy of atomic hydrogen

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  1. High precision spectroscopy of atomic hydrogen J. Alnis, A. Matveev, N. Kolachevsky, Th. Udem, T. Hänsch

  2. Energy levels Of H atoms

  3. „Hänsch curve“ Precision optical spectroscopy of H atoms H against Cs frequency measurements with 14 digits of precision Searching for the possible drift of fundamental constants (global warming analogy)

  4. 2003 Standard dye laser system for H 1S-2S spectroscopy

  5. 243 nm semiconductor laser system 40 % H excitation efficiency compared to the dye laser system

  6. Optical beat note betweenDiode &Dye laser systemssimultaneously at 486 nm and at 243 nm The narrow central peak has a broad pedestal typical for diode lasers. Optimal feedback too weak feedback too strong feedback 2 SHG and one two-photon processes are necessary to get from 972 nm to 121 nm. (Icentral/Itotal)4*4*4 =(Icentral/Itotal)64 99%power in carrior at 972 nm  50 % percent power in carrior at H excitation.

  7. Vertical FP cavityfor diode laser locking at 972 nm. Finesse 410000. FSR 1.931(1) GHz Line width < 10 Hz at 972 nm. Drift 0.2 Hz/s. Compact table-top setup 40 x 40 cm. Cavity length 7 cm. Made from single piece of Ultra Low Expansion glass (manuf. Corning). Cavity stands on 3 teflon posts and on a zerodur ring. Optically contacted super-mirrors on ULE substrates ( Advanced ThinFilms, Colorado, USA).

  8. Compact optical assembly 40 x 40 cm active vibration isolation stage. Optics for a) fiber noise compensation (AOM), b) intensity stabilisation (same AOM), c) Pound-Drewer-Hall lock, Sound proof box appearsnot to be necessary.

  9. ULE thermal expansion cross-over estimation using optical beat note between two laser systems ULE has a temperature Tc where thermal expansion coefficient becomes zero: We estimate Tc for our ULE material to be at +7 ºC. Due to practical reasons we stabilise cavity at +31 ºC.

  10. NEW IDEA!Cooling of the ULE Fabry-Perot cavity to the zero-temperature-expansion point by Peltier cooler in vacuum

  11. Optical beatnote – so slow that observable with an eye

  12. Drift of FP stabilised laser 0.1 Hz/s

  13. Fast lock-box for diode laser current feedback5MHz flat gain, two integrators, phase advance

  14. Summary • 243 nm diode laser successful but more broadband noise than dye laser. Ti:Sa laser instead of diode laser? • Mid-plane mounted vertical laser stabilisation FP cavity very successful • Proton detection instead of photon detection • New precision measurement planned autumn 2007

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