séminaire interne du groupe Atomes Froids Vendredi 08 octobre 2004
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Transcript of séminaire interne du groupe Atomes Froids Vendredi 08 octobre 2004
séminaire interne du groupe Atomes Froids
Vendredi 08 octobre 2004
Steven MOAL, Maximilien PORTIER, Jaewan KIM
Michèle LEDUC, Claude COHEN-TANNOUDJI
Determination of the s-wave scattering
length in metastable helium :
experimental results withsingle photon photoassociation
1st STEP :
TWO PHOTONS EXPERIMENT
PRINCIPLE OF EXPERIMENT
continuum
R
S + S
S + P0
1
E
r
2
5 g+
0u+
v=14
v = 0
interatomic distance
energ
y
kBT
FRUSTRATED PA vs. RAMAN TRANSITION
1
fixed
2
scanned
5g+ (v=14)
S + S
0u+ (v =
0)
Tem
pera
ture
(a.u
.)
-20 -10 0 10 20
Detuning with respect v=14 (MHz)
Tem
pera
ture
(a.u
.)
-20 -10 0 10 20
Detuning with respect v=14 (MHz)
5 g+
(v=14)
S + S
0u+ (v =
0)
1
scanned
2
fixed
-15 -10 -5 0 5 10 15
0
110-13
210-13
310-13
410-13
-20 -10 0 10 200
110-13
210-13
310-13
410-13
• a large range scan to exploreOrsay value : 11 4 nm range of –15 MHz <
< -110 MHz
• transition probabilities (FC factors) are not known precisely : too many differents combinations of relative power. • large line width of the PA laser (3 MHz) :
SOME DIFFICULTIES
-20 -10 0 10 20
510-14
110-13
1.5 10-13
210-13
2.5 10-13
310-13
3.5 10-13
-15 -10 -5 0 5 10 150
210-14
410-14
610-14
810-14
Tem
pera
ture
(a.u
.)Tem
pera
ture
(a.u
.)
Detuning with respect v=14 (MHz) Detuning with respect v=14 (MHz)
larg
e w
idth
Tem
pera
ture
(a.u
.)Tem
pera
ture
(a.u
.)
2nd STEP :
ONE PHOTON EXPERIMENT
1- MEASURE OF LOSS SIGNAL
MESURE OF LOSS SIGNAL (1)
-675 -670 -665 -660 -6550
50
100
150
200
250
300
350N
umbe
r of
Ato
ms
(a.u
.)
PA Laser Detuning (MHz)
0 50 100 150 200 250 300 350 400 450 50010-7
10-6
1x10-5
1x10-4
10-3
10-2
10-1
100 v=4
v=3v=2v=1
v=0
rela
tives
inte
nsi
ties
of
mole
cula
r lin
es
scattering length a (a0)
the loss of atoms depend of the Franck Condon factor
one idea :we can measure the relative intensities of molecular lines
• the loss measurement is too noisy for a very precise value of « a »• FC calculation is not enough precise in our case
measurement
of the scattering length « a »
BUT :
MESURE OF LOSS SIGNAL (2)
• it’s NOT very precise
• a very fast non-linear effect (some 60 ISAT)
• not good agreement with this reference
John L. Bohn and P. S. Julienne, Phys. Rev. A 60, 414 (1999)
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.450.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8line v=0
Are
a L
ose
Intensity of PA pulse (mW)
0.00 0.05 0.10 0.15 0.20 0.250.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 line v=1
Are
a L
ose
Intensity of PA pulse (mW)
ONE PHOTON EXPERIMENT
2- MEASURE OF OSCILLATION OF THE CLOUD
THE CLOUD MOVES !
when we put one photon at resonance with different Thermalization time :
0 10 20 30 40 5075
76
77
78
93.594.094.595.095.5
Offset 76.99 ±0.03Amplit 1.62 ±0.04Freq 90.03 ±0.26phase -0.94 ±0.14
X0
& Y
0 (
pix
els
)
Thermalisation time (ms)
… with the frequency of the trapthe cloud moves…
-20 0 20 40 60 80 100 120 140 160-0.1
0.0
0.1
0.2
0.3
0.4
0.5
X
pixel
Therm
= 19.5 ms
Therm = 14.4 ms
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00.0
0.5
1.0
1.5
2.0
2.5
3.0 line v = 0
y = a * x + bR^2 = 0.967 a 0.57 ±0.02b 0 ±0
Am
plit
ud
e (
pix
el)
PA Pulse Intensity (mW)
0.0 0.2 0.4 0.6 0.8 1.0 1.20.0
0.5
1.0
1.5
2.0
2.5line v = 1
y = a * x + bR^2 = 0.886 a 2.02 ±0.11b 0 ±0
Am
plit
ud
e (
pix
el)
PA Pulse Intensity (mW)
it’s linear !
slope ratio :
BUT : • the trap is harmonic.• for high intensities, the line is not at resonance because of a shift with laser intensity.
FCFC 0.3 3.54
0.572.02
0v slope1v slope
0v
1v
?
THE CLOUD MOVES ! (2)
ONE PHOTON EXPERIMENT
3- MEASURE OF THE SHIFTWITH LASER INTENSITY
DISCOVER OF A SHIFT WITH LASER INTENSITY
when we explore high power of PA beam :
-675 -670 -665 -660 -655150
200
250
300
350
400
450
Te
mp
era
ture
(p
ixe
ls^2
)
PA Laser Detuning (MHz)
line v=1 with 0.5 mW
position = -667.7 MHz
-690 -685 -680 -675 -670
200
400
600
800
1000
1200
Te
mp
era
ture
(p
ixe
ls^2
)
PA Laser Detuning (MHz)
line v=1 with 4 mW
position = -685.0 MHz
• shift of 17.3 MHz !• deformation of the line at high intensities
continuum
INTERPRETATION
one approach : A. Simoni, P. S. Julienne et al, Phys. Rev. A 66, 63406 (2002)
shiftdue to thecontinuum
shiftdue to a
bound state
El
0e
0g
Veg
v = 14 S - S
v = 0
Veg
DIRECTION OF THE SHIFT
• shift due to the bound state v=14
BLUE SHIFT
• shift due to the continuum
: energy of the continuum: energy of v=14
contribution :
if RED SHIFT
BLUE SHIFTRED SHIFT
EXPERIMENTAL SHIFT
0 1 2 3 4 5 6 7 8 9-1450
-1448
-1446
-1444
-1442
-1440
-1438
-1436
-1434 line v=0
y = a * x + bR^2 = 0.9975 a -1.54 ±0.03b -1435.67 ±0.16
Pos
ition
de
v=0
(MH
z)
Intensité du PA-Pulse (mW)
0.0 0.5 1.0 1.5 2.0 2.5-678
-676
-674
-672
-670
-668
-666
-664 line v=1
y = a * x + bR^2 = 0.96662 a -4.48 ±0.23b -665.48 ±0.22
Po
sitio
n de
v=
1 (M
Hz)
Intensité du PA-Pulse (mW)
we have a RED SHIFT for v=0always a RED SHIFT for v=1
BUT :
slope ratio : 0.2 2.91 1.544.48
0v slope1v slope
• some uncertainty on the laser intensity
difficulty in deducing absolute values of FC factor
CONCLUSION
for evaluation of Franck Codon factor :
• the measurement of loss signal : too much uncertainty• the measurement of oscillation : ratio of 3.54 0.3
we need to understand the phenomenon of oscillations
for precise value of the scattering length :
• the measurement of the light shift of the molecular line
BUT we need to finish the theory :
to calculate accurately the shifts
AFTER…
1- spectroscopy of D2
He*23S1
11S0
1083 nm
J=0
123PJ
2 2.29 GHz
29.6 GHz
to continue Raman 2 photons PA with a potentiel more adapted than 0u
+
2- optical Feshbach
to study Mott transition
3- BEC in linear lattice
to change the scattering length « a » with light