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Progress in ultra-fine birefringence measurements
Optical Search for QEDvacuum magnetic birefringenceAxion and photon Regeneration
the 94th Meeting of the SPSC – CERN – 2009-November 24
STATUS REPORT
Mathieu Durand(1), Jérôme Morville(1), Daniélé Romanini(2)
(1 )Laboratoire de Spectrométrie Ionique et Moléculaire (LASIM)UMR CNRS 5579, Université Claude Bernard-Lyon1
(2 )Laboratoire de Spectrométrie Physique (LSP)UMR CNRS 5588, Université Joseph Fourier - Grenoble
NEW
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. Hošek, M. Kràl, J. Zicha, M. Virius
ISI, ASCR, Brno, Czech Republic A. Srnka
IMEP/LAHC - INPG, 38016 Grenoble Cédex-1, France L. Duvillaret, G. Vitrant, J.M. Duchamp
IN, CNRS – UJF & INPG, BP 166, 38042 Grenoble Cédex-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'Hères, France R. Jost, S. Kassi, D. Romanini
TUL, Czech Republic M. Šulc
Warsaw University, Physics Department, Poland A. Hryczuk, K. A. Meissner
The OSQAR Experiments at CERN to probe QD & Astroparticle Physics from the Photon Interaction with a Magnetic Field
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The OSQAR Collaboration at present ► 24 Members from 10 Institutes (Cz, Fr, Po & CERN)
Ln//
Ln
LΔnλ
2π
LaserPP
Laser
2
P2
P
Matter anisotropy induces different answer with the electric field vector orientation
Entering linearly polarized Light exits elliptically polarized
Malus law for small dephasing
What is birefringence ?
3
4
The vacuum embedded in a magnetic field should also be anisotropic
20
24 B104n
22106,3n
Is predicted @ l=500 nm with the CERN dipole magnets
If T5,9B0
rad107,0 13
m15L
giving
Using High Finesse Optical Cavity
effLn2
LaserPP
R+T+Loss=1(Loss~few ppm)
R~99,999%
The medium is contained between two high reflective and low losses dielectric mirrors
outP
L
If light resonates inside the cavity (constructive interference at each round trip),Light transmitted trough the exit mirror has an effective optical pathlength of
LF2
Leff
510R1
F
with the finesse 5
Polarizer Crossed 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
birefringence
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Dn=K.E2
PolarizerCrossed polarizer
Modulated Voltage W
7
xqin
qout
yz qM
x
Using residual mirrors birefringence as an optical bias for homodyne detection
fin
fout
fM(fin,fout,qin,qout)
8
DC W component negligible high order terms
The lowest gas dephasing measurable : g
Sensitivity given by :
gσ
π
2F
I
Inoise M
2
Ω//
Gain induced by the optical bias : 410
g
MG
Experimental set-up with N2 as a gas test
l/4PolarizerModulated voltage W
DiodeLASER
IT
Lock’in detection at W
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E=0 V/mm
E=6,4 V/mm
[V] IT
I┴
[mV]
I┴ WTime (sec)
trd=147 ms F =277 000
(L=50 cm)
Time (µs)
[10-12 rad]sfgDfg
0 V/mm
2,7 V/mm
6,4 V/mm1,3 V/mm
Measured sensitivity with N2 as a gas test
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sfg = 4.10 -12 rad/Hz1/2
Allan variance plot :
9,3 V/mm
Measured sensitivity with N2 as a gas test as a function of integration time
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4
0,3
sfg = 3.10 -13 rad
Measurement of Kerr constants
KN2 = 1,438.10-25 ± 0,006 m2/V2
-Kerr constant K:
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L = 50 cml = 810 nm
Molecular gases alignmentAtomic gases distortion of electronic wavefunction
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Kerr constants of several gases
20% 80%1,64 ± 0,04
·
CO2
O2
N2
Ar
Ne
He
14
(199
7)
(198
5)
(196
7)
(200
0)
(200
5)
(200
8)
Comparison with published results
Thi
s wor
k
15
Achievement
a table top optical system for Kerr birefringence measurement in gas phase is demonstrated
sfg = 4.10 -12 rad/Hz1/2
Only the PVLAS system reaches comparable performance, based on noise analysis (4-times better, in development since 1994)
sfg = 3.10 -13 rad By averaging over 800 s, limited by the laser-cavity servo-lock system
Our 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 power
outlooks
Recall : rad107,0 13
Accommodation to the OSQAR experiment
With B0=9,5T and L=15m
Measuring in transmission (instead of reflection) :g 5
g
Detection at the shot noise levelg 2
g
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
g
All taken into accountg rad101,160 152
g
6g
Integration time of 1 hour :g 3600
g
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outlooks
Magnetic field and homodyne detection scheme
xqin
qout
y
fin
fout
B
All the setup rotates
Two possibilities
8 Hz demonstrated with the new version
Only mirrors rotates around their optical axis
maintaining high finesse properties
1818
nn nn+1nn-1
n
Spectral transmission
Constructive interferences => frequency comb nresonance
%10PP Laserout
<Dn 1kHzDn=c/2L
The finesse is defined as :
5
roundtrip
ringdown 10R1
2F
LF2
Leff
Cavity lifetime
effLn2
LaserPP
R+T+Loss=1(Loss~few ppm)
R~99,999%
outP
L
The cavity more in detailed
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Optimum : fM ~ 0,1·p/F
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Optical detection
Laser-cavity locking residual
instability
Mirror birefringence as optical bias and noise analysis