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Toward a Stark Decelerator for atoms and molecules exited into a Rydberg state. Anne Cournol, Nicolas Saquet , Jér ôme Beugnon, Nicolas Vanhaecke, Pierre Pillet. Laboratoire Aime Cotton EGC 2008. 07/03/2008. Cold atoms. Into a gas: cold means weak velocity distribution - PowerPoint PPT Presentation
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Toward a Stark Toward a Stark Decelerator for Decelerator for
atoms and molecules atoms and molecules exited into a exited into a Rydberg stateRydberg state
Anne Cournol, Nicolas Saquet, Jérôme Beugnon,Nicolas Vanhaecke, Pierre Pillet
07/03/2008Laboratoire Aime CottonEGC 2008
• Cold?
• For what?
• How to do?
Cold atomsCold atoms
Into a gas: cold means weak velocity distribution around a mean velocity
Precision measurements Quantum gases …
Laser cooling Evaporative cooling …
Cold molecules?Cold molecules?• High resolution spectroscopy (very long
interaction time)• 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)
Why ?
How ? • From cold atoms (T<1mK)• Buffer gas cooling (T<1K)• Bolztmann filter (T < 1K)• Rotating nozzle (T~1K)• Beam collision (T~1K)• Deceleration of supersonic molecular beam (T<1K)
Electric Stark decelerator (polar species): Meijer (OH,NH,ND3,CO),Tiemann (SO2), Hinds (YbF,CaF)
Optical Stark decelerator: Barker (C6H6)
Zeeman decelerator: Merkt (H,D), Raizen (Ne*,O2)
Electric Stark decelerator (Rydberg state): Merkt (Ar,H), Softley (H2)
Stark decelerationStark decelerationStark effect: -
SO2: =1.6Debye, 326 stages, L=1.8 m, HV=10kV, =400ns ∆E=0.95cm-1/stage
5.5mm
2mm
+: Huge density in phase space (conserved by deceleration)
-: Dipolar momentum of polar molecules 1Debye
Rydberg stateRydberg state
Highly excited electronic state
€
E = −1
2n2
For hydrogen atoms, level energies for Rydberg electron states are:
€
E = −1
2n2+3
2nkF
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 Rydberg states into electric fieldelectric field
m=2
18d
19d
SO2
Stark decelerator for Stark decelerator for Rydberg statesRydberg states
Rydberg states: dipolar momentum ~1000 Debye
Compact decelerator Versatile decelerator
Lower electric and shapeable field
Continius deceleration
Constant force
OutlineOutline
Supersonic beam
Rydberg Excitation
Deceleration: simulations 3D
The setupThe setup
Production of pulsedsupersonic beamExperiences
P≈10-8mbar
A supersonic beamA supersonic beam
Effusive beam Supersonic beam
Some properties of supersonic beam:• Mean velocity• Axis velocity distribution• Perpendicular velocity distribution
Sodium pulsed beamSodium pulsed beam
Cw dye laser @589 nm (Tekhnoscan on saturated absorption)
Ablation laser Nd:YAG@532nm 1.0 mJ/pulse
10 - 50 Hz
10 cm 15 cm
Detection by fluorescence induced by laser
Detection areas
Rotating sodium target
Carrying gas~1-10 bar
Time of flightTime of flight
Longitudinal velocity distribution(~10%vexp)
Parameter: ablation Parameter: ablation energyenergy
Carrying gas: Argon Pressure: 6 Bar
Parameter: ablation Parameter: ablation energyenergy
Carrying gas: Argon Pressure: 6 Bar
Parameter: Parameter: pressurepressure
Neon with ablation energy of 0.6 mJ/pulse
Perpendicular Perpendicular temperaturetemperature
L
v
Doppler measurement
Perpendicular Perpendicular temperaturetemperature
Perpendicular temperature about 1K
Doppler profile
60 MHz
0
Beam characterizationBeam characterization
• Heating effect when ablating
• Beam optimization
• Argon (v≈650 m/s)• Axis temperature ≈ 5K• Perpendicular temperature ≈ 1K
•Density ≈108atoms/cm3
Excitation toward a Excitation toward a Rydberg stateRydberg state
Laser excitation
Doubledpulsed dye
Excitation processExcitation process
3S
4P
nd
330 nm
920 nm
(18d m=2)
Ionisation
Ti:Sa
3S-4P3S-4P
Doubledpulsed dye
3S
4P
330 nm
330 nm
Ionisation
First spectrum last week
3S-4P3S-4P
170GHz
3S
4P
330 nm
330 nm
Ionisation
SimulationsSimulations
Deceleration: simulations 3D
Particle test: NaParticle test: Na• Initial state: 18d• Field : 800 V/cm• Number of electrodes: 20 pairs
3mm1mm
Beam axe
• Initial velocity: 370 m/s
• Final velocity: 0 m/s
Laser excitation
+V
-V
Experienced Experienced forceforce
Time for deceleration ~10µs
Distribution of Distribution of positionspositions
No deceleration90%
Deceleration10%
Initial cloud: 500000 atomes ∆x=2mm∆v///v//=10%, ∆v/v//=3%
ConclusionConclusion
• 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
ConclusionConclusion
• HV: ±10kV• L=1.8m• 326 stages• Efficiency: 1%• Detection by fluorescence
• HV: ±40V• L=3mm• 20 ‘stages‘• Efficiency: 10%• Ionic detection
Stark decelerator (SO2)Stark decelerator for atoms and molecules excited into a Rydberg states
• One laser to detect the molecules
• 4 lasers
OutlookOutlook
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, …
MerciMerci