Diapositive 1

1Progress in ultra-fine birefringence measurements

the 94th Meeting of the SPSC CERN 2009-November 24 STATUS REPORTMathieu Durand(1), Jrme Morville(1), Danil Romanini(2)

(1 )Laboratoire de Spectromtrie Ionique et Molculaire (LASIM)UMR CNRS 5579, Universit Claude Bernard-Lyon1 (2 )Laboratoire de Spectromtrie Physique (LSP)UMR CNRS 5588, Universit Joseph Fourier - GrenobleNEW collaborator CERN, Geneva, Switzerland P. Pugnat (now at LNCMI-CNRS), M. Schott, A. Siemko

Charles University, Faculty of Mathematics & Physics, Prague, Czech Republic M. Finger Jr., M. Finger

Czech Technical University, Faculty of Mechanical Engineering, Prague, Czech Republic J. Hoek, M. Krl, J. Zicha, M. Virius

ISI, ASCR, Brno, Czech Republic A. Srnka

IMEP/LAHC - INPG, 38016 Grenoble Cdex-1, France L. Duvillaret, G. Vitrant, J.M. Duchamp

IN, CNRS UJF & INPG, BP 166, 38042 Grenoble Cdex-9, France B. Barbara, R. Ballou, Y. Souche

LASIM , UCB Lyon1 & CNRS, 69622 Villeurbannes, FranceM. Durand, J. Morville

LSP, UJF & CNRS, 38402 Saint-Martin d'Hres, France R. Jost, S. Kassi, D. Romanini

TUL, Czech Republic M. ulc

Warsaw University, Physics Department, Poland A. Hryczuk, K. A. MeissnerThe OSQAR Experiments at CERN to probe QD & Astroparticle Physics from the Photon Interaction with a Magnetic Field2/45

The OSQAR Collaboration at present 24 Members from 10 Institutes (Cz, Fr, Po & CERN)

Matter anisotropy induces different answer with the electric field vector orientationEntering linearly polarizedLight exits elliptically polarizedMalus law for small dephasingWhat is birefringence ?334The vacuum embedded in a magnetic field should also be anisotropic

Is predicted @ l=500 nm with the CERN dipole magnetsIf

givingUsing High Finesse Optical Cavity

R+T+Loss=1(Loss~few ppm)R~99,999%The medium is contained between two high reflective and low losses dielectric mirrors

If light resonates inside the cavity (constructive interference at each round trip),Light transmitted trough the exit mirror has an effective optical pathlength of

with the finesse 55PolarizerCrossed Polarizer Voltage

Gas Recent Kerr anisotropy measurementsPhD thesis : Mathieu Durand (07/23/2009)

At this level of sensitivity, residual mirrors birefringence entirely conceals the effect of gas birefringence6Dn=K.E26PolarizerCrossed polarizerModulated Voltage W

7xqinqoutyzqMxUsing residual mirrors birefringence as an optical bias for homodyne detection

finfoutfM(fin,fout,qin,qout)78

DCW componentnegligible high order termsThe lowest gas dephasing measurable :

Sensitivity given by :

Gain induced by the optical bias :

8Experimental set-up with N2 as a gas testl/4PolarizerModulated voltage WDiodeLASERIT

Lockin detection at W

9

E=0 V/mmE=6,4 V/mm [V] IT I [mV] I WTime (sec)

trd=147 ms F =277 000(L=50 cm)Time (s)

[10-12 rad]sfgDfg0 V/mm2,7 V/mm6,4 V/mm1,3 V/mmMeasured sensitivity with N2 as a gas test10sfg = 4.10 -12 rad/Hz1/2

Allan variance plot :9,3 V/mmMeasured sensitivity with N2 as a gas test as a function of integration time1140,3sfg = 3.10 -13 radMeasurement of Kerr constants

KN2 = 1,438.10-25 0,006 m2/V2-Kerr constant K:12L = 50 cml = 810 nmMolecular gases alignmentAtomic gases distortion of electronic wavefunction13Kerr constants of several gases

20%80%1,64 0,04

CO2O2N2ArNeHe14

(1997)(1985)(1967)(2000)(2005)(2008)Comparison with published resultsThis work15Achievementa table top optical system for Kerr birefringence measurement in gas phase is demonstratedsfg = 4.10 -12 rad/Hz1/2Only the PVLAS system reaches comparable performance, based on noise analysis (4-times better, in development since 1994)sfg = 3.10 -13 radBy averaging over 800 s, limited by the laser-cavity servo-lock systemOur result constitutes the present state-of-the-art validated on a physical signal.a factor two above the shot noise level with 3 mW incident laser poweroutlooksRecall :

Accommodation to the OSQAR experimentWith B0=9,5T and L=15mMeasuring in transmission (instead of reflection) :

Detection at the shot noise level

An increase of the laser beam transverse dimension (a factor 40 with a confocal cavity of 20 m length) increases the maximal incident power and thus the shot noise level

All taken into account

Integration time of 1 hour :

1617outlooksMagnetic field and homodyne detection schemexqinqoutyfinfoutB

All the setup rotatesTwo possibilities8 Hz demonstrated with the new versionOnly mirrors rotates around their optical axismaintaining high finesse properties171818nnnn+1nn-1nSpectral transmissionConstructive interferences => frequency comb

nresonance

Dn