1. ULTRA-HIGH RESOLUTION SYNCHROTRON-BASED VUV ABSORPTION SPECTROSCOPY USING A NEW FOURIER TRANSFORM SPECTROMETER: FIRST APPLICATION TO THE ABSORPTION SPECTRA OF THE RARE GASES. MOURAD ROUDJANE, NELSON DE OLIVEIRA, DENIS JOYEUX, MICHEL VERVLÖET and LAURENT NAHON Synchrotron SOLEIL, L'orme des Merisiers, St. Aubin Bp 48, 91192 Gif sur Yvette Cedex, France. KENJI ITO Photon Factory, National Laboratory for High Energy Physics, Oho, Tsukuba, Ibaraki-ken 305, Japon International Symposium on Molecular Spectroscopy 63rd Meeting -June 16-20, 2008

2. Introduction Experimental studies of VUV spectrum of atoms and molecules Grating based spectroscopy Accuracy :  ~ 10 -6 external étalon required Large wavelength range with resolving power R ~ 250 000 Laser spectroscopy  ~ 10 -8 Restraint wavelength range New instrument, Fourier transform spectrometer, is NOW available at SOLEIL Synchrotron !!  ~ 10 -7  [40-140 nm] with R ~ 700 000

3. Experimental Setup Beam splitter, <140 nm ? FTS in the VUV range : Ok for >140 nm Wave front division (Young’s slits, Fresnel’s bimirror ) " ray bundle is separated into 2 bundles" interferences  no beam splitter required!  local spatial coherence required field limited by source brilliance (through local coherence ) Vs Amplitude division (Mach-Zehnder, Michelson) " each ray is split " interferences  low spatial coherence allowed  beam splitter mandatory field limited by beam splitter size Synchrotron Radiation required

4. Angular control Beam separator monomode, freq. stabilised HeNe Angular control beam Interferometric control beam Moving reflector: Smooth translation !! VUV side ray fan DESIRS beamline at SOLEIL Synchrotron Fresnel interferometer : only mirrors (no beamsplitter) { FTS

5. Absorption spectroscopy near the ionization threshold of rare gases Study of the Rydberg series of rare gases Ne, Ar, Kr and Xe : mp 6 1 S 0  mp 5 3/2 ns(3/2) 1, mp 5 3/2 nd(1/2) 1, mp 5 3/2 nd(3/2) 1  mp 5 1/2 ns’(1/2) 1 et mp 5 1/2 nd’(3/2) 1 (m= 2, 3, 4 and 5) Absorption cell Fluo 2p 6 ( 1 S 0 ) 3s 4s 5s 6s 3s’ 4s’ 5s’ 6s’ h h Ne at 21.8 eV (57nm) Pression = 4.5*10 -2 mbar Averaged over 56 spectrum

6. Xe@ 12.5 eV (100nm) average of 100 spectrum Kr @ 14.3 eV (87 nm), average of 71 spectrum Ar @ 15.5 eV (80nm) average of 59 spectrum Ar atom Resolvin Power  Emin= 36 µeV deconvolution Instrumental width Sinc FWHM = 22.5 µ eV NeArKrXe Fwhm = 29 µeV  = 744000 Fwhm = 22.3 µeV  = 708000 Fwhm = 20 µeV  = 708000 Fwhm = 17.8 µeV  = 702000 Instrumental width Resolution power

7. Series convergin to the first Ionization threshold (ns, nd) Voigt profile Convolution of Doppler broadening + natural broadening + Instrumental broadening + collision broadening ( negligible) Wavenumbers σ (cm -1 ) ans total FWHM The error on line position is related to the S/N : δσ noise =FWHM/2*(S/N) δσ noise / σ ~ 5* 10 -8 Kr atom

8. Calculationof the absorption cross section A(l) from Beer-Lambert formula: A(l)=N -1 ln[I 0 (l)/I(l)] Kr atom Kr + lines

9. Series convergin to the second Ionization threshold (ns’, nd’) 9 d’ 11 s’ The new fit parameters of the Fano profile (K0, K1, …..,K9  σ ab, σ as, µ s, W s, q s, σ ad, µ d, W d, q d ) lead to improved comparison with MQDT Kr atom

10. A newly-developed Fourier Transform spectrometer (FTS), based upon a wave-front division interferometer, has recently been connected to the VUV beamline DESIRS on the French synchrotron facility SOLEIL, to perform an Ultra-high resolution absorption spectroscopy in the 9- 30 eV (140- 40 nm) spectral range, The ionization threshold region of 4 noble gases (Ne, Kr, Ar, Xe) has been recorded with a constant resolving power (  ) as high as 700 000 in the range [12.5 – 22 eV], better than the previous works [1-4], The first results show a repeatability and an absolute accuracy (with external line étalon) on the Ar spectrum lines position :  /  ~ 2.10 -7 rms from run to run. Future tests should confirm such precision on the wavenumber scale for an absolute calibration of the absorption spectra, The Ultra-high resolution lead to the determination of new Fano profile parameters, which are important to improve the MQDT modeling calculations. Conclusion [1] E. B. Saloman, Phys. Chem. Ref. Data., 33. 33 (2004). [2] K. Yoshino. J. Opt. Soc. Am. 65, 9 (1970) [3] L. Minnhagen, J. Opt. Soc. Am. 63, 1185 (1973). [4] K. Ito, K. Ueda, T. Namioka, K. Yoshino and Y. Morioka, J. Opt. Soc. Am. B5, 10 (1988).

11. FTS Team Laurent Nahon: Head of the group Nelson De Oliveira Michel VervlöetDenis Joyeux International Symposium on Molecular Spectroscopy 63rd Meeting -June 16-20, 2008

12. The Next deadline for standard project: 15th September, 2008 More information, see SOLEIL synchrotron web site: http://www.synchrotron-soleil.fr/portal/page/portal/Accueil International Symposium on Molecular Spectroscopy 63rd Meeting -June 16-20, 2008