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Coherent processes in metastable helium at

room temperature

Thomas LauprêtreFabienne GoldfarbFabien Bretenaker

Laboratoire Aimé Cotton, Orsay, France

School of Physical Sciences, Jawaharlal Nehru University, Delhi, India

Rupamanjari GhoshSantosh Kumar

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Summary

• Electromagnetically Induced Transparency

• Experimental set-up• Dispersion in a cavity• Tripod system

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Electromagnetically Induced Transparency ?

• Fact:Optical transition is made transparent for

a resonant field (otherwise opaque medium)

• How it happens:A quantum interference effect, induced by

a control field on a second transition

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cp c

One optical transitionΛ system

ab

cR 2

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p

Rc b

a

ab

Electromagnetically Induced Transparency (EIT)

Width of transparency window

R

cbR

relax

cb

t

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EIT and Slow Light

• Kramers-Kronig

Strong positive dispersion

d

dn

cvg )Re(

2

Slow Light !

Kash & al, PRL, 1999: 90 m.s-1 in RbHau & al, Nautre, 1999: 17 m.s-1 in cold Na

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Summary

• EIT• Experimental set-up• Dispersion in a cavity• Tripod system

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Metastable 4He

1S0

3P1

3S1

m = -1 10

RF discharge

p p

0

12

c

c

• Lifetime ~8000s

polarization selected Λ system

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Experimental results

D

cR W2

22

W

idth

at

ha

lf m

ax

imu

m (

kH

z)

Coupling intensity (W.m-2)

Gro

up

de

lay

(µs

)

Coupling intensity (W.m-2)

Group velocity around 8 km.s-1 !Goldfarb, F. & al.,

EPL (Europhysics Letters), 2008, 82, 54002

Ghosh, J. & al., Phys.Rev.A, 2009

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Summary

• EIT• Experimental set-up• Dispersion in a cavity• Tripod system

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Dispersion in cavity• Why?

Enhance sensitivity of cavity based sensors (ring laser gyroscope…)

Positive dispersion reduces the linewidth of a resonator

• Main parameter: lifetime of photons in the cavity

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Lifetime of photons

• 2 different points of view

1) Phase velocity Resonant cavity:monochromatic field

2) Group velocityGaussian pulseΔt ∞ ?

Δt

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Experiment

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Global results

• Measured decay time ~ a few µs • ~150 ns with phase velocity

Group velocity !

τcav

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Summary

• EIT• Experimental set-up• Dispersion in a cavity• Tripod system

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Tripod system

1S0

3P0

3S1

RF discharge

m = -1 10

Santosh Kumar, School of Physical Sciences, Jawaharlal Nehru University, Delhi, India

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Tripod system

ΩP ΩPΩC

my = -1 10

0

B

(kHz)

ΩC ΩCΩP

my = -1 10

0

B

B

Laser

π

σ

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Outlook

• Negative dispersion inside our cavityFast lightNegative group velocity

• Further investigations on Tripod system

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0<vg <c c<vg vg <-c -c<vg <0