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 NAHONSynchrotron SOLEIL, L'orme des Merisiers, St. Aubin Bp 48, 91192 Gif sur Yvette Cedex, France.

KENJI ITOPhoton Factory, National Laboratory for High Energy Physics, Oho, Tsukuba, Ibaraki-ken 305, Japon

International Symposium on Molecular Spectroscopy 63rd Meeting -June 16-20, 2008

IntroductionExperimental 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

Experimental SetupBeam 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 )

VsAmplitude 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

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

Absorption spectroscopy near the ionization threshold

of rare gasesStudy of the Rydberg series of rare gases Ne, Ar, Kr and Xe :

mp6 1S0 mp53/2ns(3/2)1, mp5

3/2nd(1/2)1, mp53/2nd(3/2)1

mp5

1/2ns’(1/2)1 et mp51/2nd’(3/2)1 (m= 2, 3, 4 and 5)

Absorption cell

Fluo2p6 (1S0)

3s

4s

5s

6s

3s’

4s’

5s’

6s’

hh

Ne at 21.8 eV (57nm)Pression = 4.5*10-2 mbarAveraged over 56 spectrum

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

Ne Ar Kr Xe

Fwhm = 29 µeV = 744000

Fwhm = 22.3 µeV

= 708000

Fwhm = 20 µeV = 708000

Fwhm = 17.8 µeV

= 702000Instrumental widthResolution power

Series convergin to the first Ionization threshold (ns, nd)

80

60

40

20

0

-20

-40

x1

0-3

180.20180.15180.10180.05180.00x10

3

3.0

2.0

1.0

0.0

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 :

δσnoise =FWHM/2*(S/N)

δσnoise/ σ ~ 5* 10-8

Kr atom

Calculationof the absorption cross section A(l) from Beer-Lambert formula: A(l)=N-1 ln[I0(l)/I(l)]

800

600

400

200

0

Ab

sorp

tion

Cro

ss S

ect

ion

(M

b)

118x103

116114112

Wavenumbers(cm-1)

Kr atom

Kr + lines

Series convergin to the second Ionization threshold (ns’, nd’)

400

300

200

100

0

ph

oto

ab

so

rptio

n c

ross s

ectio

n (

Mb

)

5.85.65.45.25.04.84.6V_1/2

Curve Fit Resultslun. 5 mai 2008 18:25:57

Fit Type: least squares fitFunction: FanoProfileModel: fit_w_absY data: root:w_abs[191619,219397]X data: root:wave_nu[191619,219397]Coefficient values ± one standard deviation

K0 =18.95 ± 0.123K1 =0.25464 ± 0.0348K2 =0.099691 ± 1.54e-005K3 =0.0091391 ± 4.82e-005K4 =34.938 ± 2.39K5 =22.654 ± 0.158K6 =0.2241 ± 0.000206K7 =0.16641 ± 0.000627K8 =2.0057 ± 0.00849

9 d’

11 s’

The new fit parameters of the Fano profile (K0, K1, …..,K9 σab, σas,

µs, Ws , qs , σad, µd, Wd , qd ) lead to improved comparison with MQDT

Kr atom

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).

FTS Team

Laurent Nahon: Head of the group

Nelson De Oliveira

Michel Vervlöet Denis Joyeux

International Symposium on Molecular Spectroscopy 63rd Meeting -June 16-20, 2008

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