Download Toward a Rydberg-Stark Decelerator

Toward a Stark
Decelerator for atoms
and molecules exited
into a Rydberg state
Anne Cournol, Nicolas Saquet, Jérôme Beugnon,
Nicolas Vanhaecke, Pierre Pillet
07/03/2008
Laboratoire Aime Cotton
EGC 2008
Cold atoms
• Cold?
Into a gas: cold means weak velocity distribution
around a mean velocity
• For what?
 Precision measurements
 Quantum gases
…
• How to do?
 Laser cooling
 Evaporative cooling
…
Cold molecules?
Why ? • High resolution spectroscopy (very long interaction time)
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Cold chemistry
Polar molecules : dipole - dipole interaction
Variation of fundamental constants with time (Ye OH)
Parity violation (DeMille BaF,HSiO)
EDM (DeMille PbO, Hinds YbF)
Electric Stark decelerator (polar species): Meijer
(OH,NH,ND3,CO),Tiemann (SO2), Hinds (YbF,CaF)
How ? • From cold atoms (T<1mK)
• Buffer
gas cooling Barker
(T<1K) (C6H6)
Optical Stark
decelerator:
• Bolztmann filter (T < 1K)
Rotating nozzle
(T~1K)
Zeeman •decelerator:
Merkt
(H,D), Raizen (Ne*,O2)
• Beam collision (T~1K)
• Deceleration
of supersonic
Electric Stark
decelerator
(Rydbergmolecular
state): beam
Merkt(T<1K)
(Ar,H), Softley
(H2)
Stark deceleration
Stark effect: -
2mm
5.5mm
SO2: =1.6Debye,
326 stages, L=1.8 m,
HV=10kV, =400ns
∆E=0.95cm-1/stage
+: Huge density in phase space (conserved by deceleration)
-: Dipolar momentum of polar molecules  1Debye
Rydberg state
Highly excited electronic state
For hydrogen atoms, level energies for
Rydberg electron states are:
1
E  2
2n
1
3
E   2  nkF
2n
2
Particle in zero field
Particle in electric field
(n 1 m )  k  n 1 m
Stark effect

Dipolar momentum ≈1000 Debye for n=18
Rydberg states into
electric field
19d
SO2
18d
m=2
Stark decelerator for
Rydberg states
Rydberg states: dipolar momentum ~1000 Debye
Lower electric and shapeable field
 Constant force
Continius deceleration
Compact decelerator
Versatile decelerator
Outline
Supersonic beam
Deceleration: simulations
3D
Rydberg Excitation
The setup
P≈10-8mbar
Experiences
Production of pulsed
supersonic beam
A supersonic beam
Some properties of supersonic beam:
• Mean velocity
• Axis velocity distribution
• Perpendicular velocity distribution
Effusive beam
Supersonic beam
Sodium pulsed beam
Detection by fluorescence induced by laser
Rotating sodium
target
10 cm
Detection areas
10 - 50 Hz
Carrying gas
~1-10 bar
Ablation laser
Nd:YAG@532nm
1.0 mJ/pulse
Cw dye laser @589 nm
(Tekhnoscan on saturated
absorption)
Time of flight
Longitudinal velocity distribution
(~10%vexp)
Parameter: ablation
energy
Carrying gas: Argon Pressure: 6 Bar
Parameter: ablation
energy
Carrying gas: Argon Pressure: 6 Bar
Parameter: pressure
Neon with ablation energy
of 0.6 mJ/pulse
Perpendicular
temperature
Doppler measurement
v
L
Perpendicular
temperature
Doppler profile
60 MHz
0
Perpendicular temperature about 1K
Beam characterization
• Heating effect when ablating
• Beam optimization
• Argon (v≈650 m/s)
• Axis temperature ≈ 5K
• Perpendicular temperature ≈ 1K
•Density ≈108atoms/cm3
Excitation toward a
Rydberg state
Laser excitation
Excitation process
Ionisation
nd
Ti:Sa
920 nm
4P
Doubled
pulsed dye
(18d m=2)
330 nm
3S
3S-4P
First spectrum last week
330 nm
Ionisation
Doubled
pulsed dye
4P
330 nm
3S
3S-4P
330 nm
Ionisation
4P
330 nm
3S
170GHz
Simulations
Deceleration: simulations 3D
Particle test: Na
• Initial state: 18d
• Initial velocity: 370 m/s
• Final velocity: 0 m/s
• Field : 800 V/cm
+V
• Number of electrodes:
20 pairs
Beam axe
-V
Laser excitation
1mm
Experienced force
Time for deceleration ~10µs
Distribution of positions
Initial cloud: 500000 atomes
∆x=2mm
∆v///v//=10%, ∆v/v//=3%
Deceleration
10%
No deceleration
90%
Conclusion
• Supersonic beam is characterized
• Excitation toward a Rydberg state is in
process
• Simulations show we can stop a cloud
of sodium atoms flying initially at
370m/s in 3mm
Conclusion
Stark decelerator (SO2)
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HV: ±10kV
L=1.8m
326 stages
Efficiency: 1%
Detection by fluorescence
• One laser to detect the
molecules
Stark decelerator for atoms
and molecules excited into a
Rydberg states
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HV: ±40V
L=3mm
20 ‘stages‘
Efficiency: 10%
Ionic detection
• 4 lasers
Outlook
Short time:
› Autumn: Rydberg excitation
› End of year: Proof of deceleration
with 4 electrodes
› Spring: Na at standstill
Long time:
Production of cold Na2, NaH, O, H2O, …
Merci